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	$89.39	12.447%	$100.5164	$100.52	$100.50	$100.50
Purchase #2	$145.83	12.862%	$164.5867	$164.59	$164.60	$164.60
Purchase #3	$156.66	12.154%	$175.7005	$175.70	$175.70	$175.70
Purchase #4	$84.80	12.781%	$95.6383	$95.64	$95.65	$95.60
Purchase #5	$246.43	10.210%	$271.5905	$271.59	$271.60	$271.60
Purchase #6	$60.62	11.323%	$67.484	$67.48	$67.50	$67.50
Purchase #7	$240.91	6.300%	$256.0873	$256.09	$256.10	$256.10
7 purchase totals =	$1,024.64		$1,131.6037	$1,131.61	$1,131.65	$1,131.60