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	$103.93	7.146%	$111.3568	$111.36	$111.35	$111.40
Purchase #2	$51.92	13.532%	$58.9458	$58.95	$58.95	$58.90
Purchase #3	$247.65	8.130%	$267.7839	$267.78	$267.80	$267.80
Purchase #4	$151.79	9.690%	$166.4985	$166.50	$166.50	$166.50
Purchase #5	$90.55	10.736%	$100.2714	$100.27	$100.25	$100.30
Purchase #6	$69.31	13.497%	$78.6648	$78.66	$78.65	$78.70
Purchase #7	$152.58	12.580%	$171.7746	$171.77	$171.75	$171.80
7 purchase totals =	$867.73		$955.2958	$955.29	$955.25	$955.40