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	$78.25	12.624%	$88.1283	$88.13	$88.15	$88.10
Purchase #2	$156.70	11.251%	$174.3303	$174.33	$174.35	$174.30
Purchase #3	$119.71	10.426%	$132.191	$132.19	$132.20	$132.20
Purchase #4	$146.38	3.448%	$151.4272	$151.43	$151.45	$151.40
Purchase #5	$78.81	13.695%	$89.603	$89.60	$89.60	$89.60
Purchase #6	$244.68	7.817%	$263.8066	$263.81	$263.80	$263.80
Purchase #7	$131.66	5.814%	$139.3147	$139.31	$139.30	$139.30
7 purchase totals =	$956.19		$1,038.8011	$1,038.80	$1,038.85	$1,038.70