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	$72.76	7.484%	$78.2054	$78.21	$78.20	$78.20
Purchase #2	$151.51	13.662%	$172.2093	$172.21	$172.20	$172.20
Purchase #3	$27.70	13.241%	$31.3678	$31.37	$31.35	$31.40
Purchase #4	$24.72	6.517%	$26.331	$26.33	$26.35	$26.30
Purchase #5	$146.86	6.541%	$156.4661	$156.47	$156.45	$156.50
Purchase #6	$90.81	3.164%	$93.6832	$93.68	$93.70	$93.70
Purchase #7	$81.88	8.129%	$88.536	$88.54	$88.55	$88.50
7 purchase totals =	$596.24		$646.7988	$646.81	$646.80	$646.80