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	$199.49	6.521%	$212.4987	$212.50	$212.50	$212.50
Purchase #2	$25.36	12.870%	$28.6238	$28.62	$28.60	$28.60
Purchase #3	$155.84	9.574%	$170.7601	$170.76	$170.75	$170.80
Purchase #4	$68.76	3.683%	$71.2924	$71.29	$71.30	$71.30
Purchase #5	$215.84	3.767%	$223.9707	$223.97	$223.95	$224.00
Purchase #6	$33.42	12.168%	$37.4865	$37.49	$37.50	$37.50
Purchase #7	$246.89	9.873%	$271.2654	$271.27	$271.25	$271.30
7 purchase totals =	$945.60		$1,015.8976	$1,015.90	$1,015.85	$1,016.00