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	$88.68	12.231%	$99.5265	$99.53	$99.55	$99.50
Purchase #2	$119.58	7.358%	$128.3787	$128.38	$128.40	$128.40
Purchase #3	$90.31	10.191%	$99.5135	$99.51	$99.50	$99.50
Purchase #4	$145.91	13.406%	$165.4707	$165.47	$165.45	$165.50
Purchase #5	$106.71	3.345%	$110.2794	$110.28	$110.30	$110.30
Purchase #6	$179.62	3.790%	$186.4276	$186.43	$186.45	$186.40
Purchase #7	$140.31	10.279%	$154.7325	$154.73	$154.75	$154.70
7 purchase totals =	$871.12		$944.3289	$944.33	$944.40	$944.30