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	$110.52	11.755%	$123.5116	$123.51	$123.50	$123.50
Purchase #2	$67.67	6.822%	$72.2864	$72.29	$72.30	$72.30
Purchase #3	$121.32	5.522%	$128.0193	$128.02	$128.00	$128.00
Purchase #4	$175.48	11.769%	$196.1322	$196.13	$196.15	$196.10
Purchase #5	$132.95	8.394%	$144.1098	$144.11	$144.10	$144.10
Purchase #6	$123.85	12.242%	$139.0117	$139.01	$139.00	$139.00
Purchase #7	$247.45	11.322%	$275.4663	$275.47	$275.45	$275.50
7 purchase totals =	$979.24		$1,078.5373	$1,078.54	$1,078.50	$1,078.50