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	$71.52	12.567%	$80.5079	$80.51	$80.50	$80.50
Purchase #2	$70.41	9.428%	$77.0483	$77.05	$77.05	$77.00
Purchase #3	$230.89	11.272%	$256.9159	$256.92	$256.90	$256.90
Purchase #4	$232.91	9.584%	$255.2321	$255.23	$255.25	$255.20
Purchase #5	$147.35	6.712%	$157.2401	$157.24	$157.25	$157.20
Purchase #6	$160.52	6.674%	$171.2331	$171.23	$171.25	$171.20
Purchase #7	$127.95	12.134%	$143.4755	$143.48	$143.50	$143.50
7 purchase totals =	$1,041.55		$1,141.6529	$1,141.66	$1,141.70	$1,141.50