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	$66.73	7.282%	$71.5893	$71.59	$71.60	$71.60
Purchase #2	$101.33	8.393%	$109.8346	$109.83	$109.85	$109.80
Purchase #3	$145.79	9.699%	$159.9302	$159.93	$159.95	$159.90
Purchase #4	$243.71	4.505%	$254.6891	$254.69	$254.70	$254.70
Purchase #5	$5.65	12.375%	$6.3492	$6.35	$6.35	$6.30
Purchase #6	$57.52	3.594%	$59.5873	$59.59	$59.60	$59.60
Purchase #7	$72.31	5.540%	$76.316	$76.32	$76.30	$76.30
7 purchase totals =	$693.04		$738.2957	$738.30	$738.35	$738.20