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	$128.90	12.186%	$144.6078	$144.61	$144.60	$144.60
Purchase #2	$17.66	13.822%	$20.101	$20.10	$20.10	$20.10
Purchase #3	$88.74	7.540%	$95.431	$95.43	$95.45	$95.40
Purchase #4	$125.56	10.689%	$138.9811	$138.98	$139.00	$139.00
Purchase #5	$47.57	13.791%	$54.1304	$54.13	$54.15	$54.10
Purchase #6	$6.53	13.776%	$7.4296	$7.43	$7.45	$7.40
Purchase #7	$189.51	7.444%	$203.6171	$203.62	$203.60	$203.60
7 purchase totals =	$604.47		$664.2980	$664.30	$664.35	$664.20