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	$243.25	4.234%	$253.5492	$253.55	$253.55	$253.50
Purchase #2	$18.73	12.779%	$21.1235	$21.12	$21.10	$21.10
Purchase #3	$170.44	4.387%	$177.9172	$177.92	$177.90	$177.90
Purchase #4	$234.37	8.788%	$254.9664	$254.97	$254.95	$255.00
Purchase #5	$202.51	7.345%	$217.3844	$217.38	$217.40	$217.40
Purchase #6	$35.90	13.590%	$40.7788	$40.78	$40.80	$40.80
Purchase #7	$48.70	11.108%	$54.1096	$54.11	$54.10	$54.10
7 purchase totals =	$953.90		$1,019.8291	$1,019.83	$1,019.80	$1,019.80