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	$238.36	4.602%	$249.3293	$249.33	$249.35	$249.30
Purchase #2	$95.62	7.562%	$102.8508	$102.85	$102.85	$102.90
Purchase #3	$108.45	9.817%	$119.0965	$119.10	$119.10	$119.10
Purchase #4	$250.84	13.130%	$283.7753	$283.78	$283.80	$283.80
Purchase #5	$121.29	7.843%	$130.8028	$130.80	$130.80	$130.80
Purchase #6	$233.53	9.595%	$255.9372	$255.94	$255.95	$255.90
Purchase #7	$49.56	11.162%	$55.0919	$55.09	$55.10	$55.10
7 purchase totals =	$1,097.65		$1,196.8838	$1,196.89	$1,196.95	$1,196.90