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	$92.30	10.759%	$102.2306	$102.23	$102.25	$102.20
Purchase #2	$203.60	12.605%	$229.2638	$229.26	$229.25	$229.30
Purchase #3	$119.31	6.113%	$126.6034	$126.60	$126.60	$126.60
Purchase #4	$82.87	8.477%	$89.8949	$89.89	$89.90	$89.90
Purchase #5	$91.59	7.830%	$98.7615	$98.76	$98.75	$98.80
Purchase #6	$128.41	4.487%	$134.1718	$134.17	$134.15	$134.20
Purchase #7	$43.89	13.301%	$49.7278	$49.73	$49.75	$49.70
7 purchase totals =	$761.97		$830.6538	$830.64	$830.65	$830.70