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	$83.83	7.800%	$90.3687	$90.37	$90.35	$90.40
Purchase #2	$92.37	9.156%	$100.8274	$100.83	$100.85	$100.80
Purchase #3	$128.35	8.698%	$139.5139	$139.51	$139.50	$139.50
Purchase #4	$110.70	13.390%	$125.5227	$125.52	$125.50	$125.50
Purchase #5	$46.32	9.368%	$50.6593	$50.66	$50.65	$50.70
Purchase #6	$101.45	4.628%	$106.1451	$106.15	$106.15	$106.10
Purchase #7	$216.92	12.527%	$244.0936	$244.09	$244.10	$244.10
7 purchase totals =	$779.94		$857.1307	$857.13	$857.10	$857.10