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	$6.61	9.838%	$7.2603	$7.26	$7.25	$7.30
Purchase #2	$230.51	10.743%	$255.2737	$255.27	$255.25	$255.30
Purchase #3	$209.36	8.591%	$227.3461	$227.35	$227.35	$227.30
Purchase #4	$5.75	12.139%	$6.448	$6.45	$6.45	$6.40
Purchase #5	$64.47	11.795%	$72.0742	$72.07	$72.05	$72.10
Purchase #6	$61.66	7.785%	$66.4602	$66.46	$66.45	$66.50
Purchase #7	$215.84	11.333%	$240.3011	$240.30	$240.30	$240.30
7 purchase totals =	$794.20		$875.1636	$875.16	$875.10	$875.20