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	$37.45	12.289%	$42.0522	$42.05	$42.05	$42.10
Purchase #2	$56.43	5.168%	$59.3463	$59.35	$59.35	$59.30
Purchase #3	$11.69	11.781%	$13.0672	$13.07	$13.05	$13.10
Purchase #4	$120.33	9.251%	$131.4617	$131.46	$131.45	$131.50
Purchase #5	$142.89	11.481%	$159.2952	$159.30	$159.30	$159.30
Purchase #6	$44.84	13.493%	$50.8903	$50.89	$50.90	$50.90
Purchase #7	$156.34	11.558%	$174.4098	$174.41	$174.40	$174.40
7 purchase totals =	$569.97		$630.5227	$630.53	$630.50	$630.60