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	$48.62	12.216%	$54.5594	$54.56	$54.55	$54.60
Purchase #2	$35.95	13.517%	$40.8094	$40.81	$40.80	$40.80
Purchase #3	$16.68	10.773%	$18.4769	$18.48	$18.50	$18.50
Purchase #4	$132.73	8.119%	$143.5063	$143.51	$143.50	$143.50
Purchase #5	$185.77	12.600%	$209.177	$209.18	$209.20	$209.20
Purchase #6	$141.61	7.641%	$152.4304	$152.43	$152.45	$152.40
Purchase #7	$220.95	12.741%	$249.1012	$249.10	$249.10	$249.10
7 purchase totals =	$782.31		$868.0606	$868.07	$868.10	$868.10