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	$248.80	12.473%	$279.8328	$279.83	$279.85	$279.80
Purchase #2	$165.44	6.292%	$175.8495	$175.85	$175.85	$175.80
Purchase #3	$247.66	10.843%	$274.5138	$274.51	$274.50	$274.50
Purchase #4	$200.65	11.410%	$223.5442	$223.54	$223.55	$223.50
Purchase #5	$89.52	13.230%	$101.3635	$101.36	$101.35	$101.40
Purchase #6	$197.29	13.447%	$223.8196	$223.82	$223.80	$223.80
Purchase #7	$141.77	3.326%	$146.4853	$146.49	$146.50	$146.50
7 purchase totals =	$1,291.13		$1,425.4087	$1,425.40	$1,425.40	$1,425.30