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	$235.37	6.191%	$249.9418	$249.94	$249.95	$249.90
Purchase #2	$98.33	10.529%	$108.6832	$108.68	$108.70	$108.70
Purchase #3	$100.47	10.314%	$110.8325	$110.83	$110.85	$110.80
Purchase #4	$103.25	8.142%	$111.6566	$111.66	$111.65	$111.70
Purchase #5	$155.76	6.805%	$166.3595	$166.36	$166.35	$166.40
Purchase #6	$30.53	5.167%	$32.1075	$32.11	$32.10	$32.10
Purchase #7	$83.67	8.834%	$91.0614	$91.06	$91.05	$91.10
7 purchase totals =	$807.38		$870.6425	$870.64	$870.65	$870.70