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	$250.78	11.426%	$279.4341	$279.43	$279.45	$279.40
Purchase #2	$243.43	9.140%	$265.6795	$265.68	$265.70	$265.70
Purchase #3	$45.54	12.855%	$51.3942	$51.39	$51.40	$51.40
Purchase #4	$44.94	11.468%	$50.0937	$50.09	$50.10	$50.10
Purchase #5	$203.76	9.486%	$223.0887	$223.09	$223.10	$223.10
Purchase #6	$245.32	4.128%	$255.4468	$255.45	$255.45	$255.40
Purchase #7	$238.67	7.349%	$256.2099	$256.21	$256.20	$256.20
7 purchase totals =	$1,272.44		$1,381.3469	$1,381.34	$1,381.40	$1,381.30