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	$231.58	8.163%	$250.4839	$250.48	$250.50	$250.50
Purchase #2	$232.96	13.597%	$264.6356	$264.64	$264.65	$264.60
Purchase #3	$228.94	12.136%	$256.7242	$256.72	$256.70	$256.70
Purchase #4	$93.84	7.242%	$100.6359	$100.64	$100.65	$100.60
Purchase #5	$167.38	13.293%	$189.6298	$189.63	$189.65	$189.60
Purchase #6	$170.60	5.342%	$179.7135	$179.71	$179.70	$179.70
Purchase #7	$32.98	13.352%	$37.3835	$37.38	$37.40	$37.40
7 purchase totals =	$1,158.28		$1,279.2064	$1,279.20	$1,279.25	$1,279.10