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	$31.29	3.657%	$32.4343	$32.43	$32.45	$32.40
Purchase #2	$129.83	11.778%	$145.1214	$145.12	$145.10	$145.10
Purchase #3	$214.34	3.641%	$222.1441	$222.14	$222.15	$222.10
Purchase #4	$131.76	12.596%	$148.3565	$148.36	$148.35	$148.40
Purchase #5	$92.57	13.276%	$104.8596	$104.86	$104.85	$104.90
Purchase #6	$103.53	4.873%	$108.575	$108.58	$108.60	$108.60
Purchase #7	$44.85	12.383%	$50.4038	$50.40	$50.40	$50.40
7 purchase totals =	$748.17		$811.8947	$811.89	$811.90	$811.90