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	$244.65	12.634%	$275.5591	$275.56	$275.55	$275.60
Purchase #2	$139.83	11.191%	$155.4784	$155.48	$155.50	$155.50
Purchase #3	$49.73	7.606%	$53.5125	$53.51	$53.50	$53.50
Purchase #4	$227.60	7.340%	$244.3058	$244.31	$244.30	$244.30
Purchase #5	$122.95	9.813%	$135.0151	$135.02	$135.00	$135.00
Purchase #6	$39.80	8.305%	$43.1054	$43.11	$43.10	$43.10
Purchase #7	$188.85	8.175%	$204.2885	$204.29	$204.30	$204.30
7 purchase totals =	$1,013.41		$1,111.2648	$1,111.28	$1,111.25	$1,111.30