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	$12.72	10.781%	$14.0913	$14.09	$14.10	$14.10
Purchase #2	$96.64	7.401%	$103.7923	$103.79	$103.80	$103.80
Purchase #3	$247.90	11.149%	$275.5384	$275.54	$275.55	$275.50
Purchase #4	$132.79	9.736%	$145.7184	$145.72	$145.70	$145.70
Purchase #5	$75.83	12.382%	$85.2193	$85.22	$85.20	$85.20
Purchase #6	$219.89	4.220%	$229.1694	$229.17	$229.15	$229.20
Purchase #7	$105.29	13.366%	$119.3631	$119.36	$119.35	$119.40
7 purchase totals =	$891.06		$972.8922	$972.89	$972.85	$972.90