Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$95.46	9.293%	$104.3311	$104.33	$104.35	$104.30
Purchase #2	$91.76	12.290%	$103.0373	$103.04	$103.05	$103.00
Purchase #3	$58.29	10.494%	$64.407	$64.41	$64.40	$64.40
Purchase #4	$104.43	7.226%	$111.9761	$111.98	$112.00	$112.00
Purchase #5	$143.97	11.771%	$160.9167	$160.92	$160.90	$160.90
Purchase #6	$123.61	10.574%	$136.6805	$136.68	$136.70	$136.70
Purchase #7	$209.66	6.647%	$223.5961	$223.60	$223.60	$223.60
7 purchase totals =	$827.18		$904.9448	$904.96	$905.00	$904.90