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	$221.29	8.805%	$240.7746	$240.77	$240.75	$240.80
Purchase #2	$52.42	12.804%	$59.1319	$59.13	$59.15	$59.10
Purchase #3	$135.76	11.862%	$151.8639	$151.86	$151.85	$151.90
Purchase #4	$127.25	7.784%	$137.1551	$137.16	$137.15	$137.20
Purchase #5	$121.51	12.699%	$136.9406	$136.94	$136.95	$136.90
Purchase #6	$131.98	8.108%	$142.6809	$142.68	$142.70	$142.70
Purchase #7	$147.47	13.645%	$167.5923	$167.59	$167.60	$167.60
7 purchase totals =	$937.68		$1,036.1393	$1,036.13	$1,036.15	$1,036.20