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	$43.48	3.853%	$45.1553	$45.16	$45.15	$45.20
Purchase #2	$147.59	8.816%	$160.6015	$160.60	$160.60	$160.60
Purchase #3	$234.90	7.535%	$252.5997	$252.60	$252.60	$252.60
Purchase #4	$54.78	8.194%	$59.2687	$59.27	$59.25	$59.30
Purchase #5	$120.32	7.631%	$129.5016	$129.50	$129.50	$129.50
Purchase #6	$119.78	3.719%	$124.2346	$124.23	$124.25	$124.20
Purchase #7	$46.35	8.111%	$50.1094	$50.11	$50.10	$50.10
7 purchase totals =	$767.20		$821.4708	$821.47	$821.45	$821.50