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	$225.38	13.725%	$256.3134	$256.31	$256.30	$256.30
Purchase #2	$51.30	12.453%	$57.6884	$57.69	$57.70	$57.70
Purchase #3	$149.68	8.676%	$162.6662	$162.67	$162.65	$162.70
Purchase #4	$96.33	4.442%	$100.609	$100.61	$100.60	$100.60
Purchase #5	$125.38	12.339%	$140.8506	$140.85	$140.85	$140.90
Purchase #6	$248.66	12.264%	$279.1557	$279.16	$279.15	$279.20
Purchase #7	$244.74	13.769%	$278.4383	$278.44	$278.45	$278.40
7 purchase totals =	$1,141.47		$1,275.7216	$1,275.73	$1,275.70	$1,275.80