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	$243.73	12.860%	$275.0737	$275.07	$275.05	$275.10
Purchase #2	$55.78	9.209%	$60.9168	$60.92	$60.90	$60.90
Purchase #3	$216.33	11.814%	$241.8872	$241.89	$241.90	$241.90
Purchase #4	$226.26	13.290%	$256.33	$256.33	$256.35	$256.30
Purchase #5	$52.26	11.825%	$58.4397	$58.44	$58.45	$58.40
Purchase #6	$217.40	12.172%	$243.8619	$243.86	$243.85	$243.90
Purchase #7	$116.37	8.596%	$126.3732	$126.37	$126.35	$126.40
7 purchase totals =	$1,128.13		$1,262.8825	$1,262.88	$1,262.85	$1,262.90