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	$41.90	11.590%	$46.7562	$46.76	$46.75	$46.80
Purchase #2	$37.49	12.416%	$42.1448	$42.14	$42.15	$42.10
Purchase #3	$195.81	11.509%	$218.3458	$218.35	$218.35	$218.30
Purchase #4	$181.40	4.669%	$189.8696	$189.87	$189.85	$189.90
Purchase #5	$145.93	13.692%	$165.9107	$165.91	$165.90	$165.90
Purchase #6	$85.69	5.282%	$90.2161	$90.22	$90.20	$90.20
Purchase #7	$126.79	9.867%	$139.3004	$139.30	$139.30	$139.30
7 purchase totals =	$815.01		$892.5436	$892.55	$892.50	$892.50