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	$124.44	9.656%	$136.4559	$136.46	$136.45	$136.50
Purchase #2	$36.79	7.572%	$39.5757	$39.58	$39.60	$39.60
Purchase #3	$234.32	9.529%	$256.6484	$256.65	$256.65	$256.60
Purchase #4	$87.95	4.204%	$91.6474	$91.65	$91.65	$91.60
Purchase #5	$87.68	13.842%	$99.8167	$99.82	$99.80	$99.80
Purchase #6	$63.69	11.713%	$71.15	$71.15	$71.15	$71.20
Purchase #7	$64.28	3.132%	$66.2932	$66.29	$66.30	$66.30
7 purchase totals =	$699.15		$761.5873	$761.60	$761.60	$761.60