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	$242.66	12.647%	$273.3492	$273.35	$273.35	$273.30
Purchase #2	$142.79	11.560%	$159.2965	$159.30	$159.30	$159.30
Purchase #3	$143.61	3.864%	$149.1591	$149.16	$149.15	$149.20
Purchase #4	$141.51	4.222%	$147.4846	$147.48	$147.50	$147.50
Purchase #5	$247.28	10.864%	$274.1445	$274.14	$274.15	$274.10
Purchase #6	$32.54	11.164%	$36.1728	$36.17	$36.15	$36.20
Purchase #7	$121.65	5.176%	$127.9466	$127.95	$127.95	$127.90
7 purchase totals =	$1,072.04		$1,167.5533	$1,167.55	$1,167.55	$1,167.50