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	$224.78	12.580%	$253.0573	$253.06	$253.05	$253.10
Purchase #2	$79.62	7.420%	$85.5278	$85.53	$85.55	$85.50
Purchase #3	$53.29	5.830%	$56.3968	$56.40	$56.40	$56.40
Purchase #4	$133.74	4.179%	$139.329	$139.33	$139.35	$139.30
Purchase #5	$142.89	8.748%	$155.39	$155.39	$155.40	$155.40
Purchase #6	$87.46	4.385%	$91.2951	$91.30	$91.30	$91.30
Purchase #7	$140.44	9.765%	$154.154	$154.15	$154.15	$154.20
7 purchase totals =	$862.22		$935.1500	$935.16	$935.20	$935.20