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	$17.53	3.507%	$18.1448	$18.14	$18.15	$18.10
Purchase #2	$122.77	8.618%	$133.3503	$133.35	$133.35	$133.40
Purchase #3	$93.58	13.734%	$106.4323	$106.43	$106.45	$106.40
Purchase #4	$81.89	10.102%	$90.1625	$90.16	$90.15	$90.20
Purchase #5	$13.96	3.753%	$14.4839	$14.48	$14.50	$14.50
Purchase #6	$54.28	8.854%	$59.086	$59.09	$59.10	$59.10
Purchase #7	$222.72	10.336%	$245.7403	$245.74	$245.75	$245.70
7 purchase totals =	$606.73		$667.4001	$667.39	$667.45	$667.40