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	$16.65	12.575%	$18.7437	$18.74	$18.75	$18.70
Purchase #2	$83.33	8.814%	$90.6747	$90.67	$90.65	$90.70
Purchase #3	$199.79	12.610%	$224.9835	$224.98	$225.00	$225.00
Purchase #4	$145.50	11.313%	$161.9604	$161.96	$161.95	$162.00
Purchase #5	$165.67	4.238%	$172.6911	$172.69	$172.70	$172.70
Purchase #6	$182.66	7.313%	$196.0179	$196.02	$196.00	$196.00
Purchase #7	$61.85	4.624%	$64.7099	$64.71	$64.70	$64.70
7 purchase totals =	$855.45		$929.7812	$929.77	$929.75	$929.80