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	$66.82	7.370%	$71.7446	$71.74	$71.75	$71.70
Purchase #2	$88.36	12.222%	$99.1594	$99.16	$99.15	$99.20
Purchase #3	$108.44	9.192%	$118.4078	$118.41	$118.40	$118.40
Purchase #4	$138.46	3.790%	$143.7076	$143.71	$143.70	$143.70
Purchase #5	$172.60	3.639%	$178.8809	$178.88	$178.90	$178.90
Purchase #6	$140.92	6.275%	$149.7627	$149.76	$149.75	$149.80
Purchase #7	$142.41	7.399%	$152.9469	$152.95	$152.95	$152.90
7 purchase totals =	$858.01		$914.6099	$914.61	$914.60	$914.60