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	$13.52	13.328%	$15.3219	$15.32	$15.30	$15.30
Purchase #2	$175.77	5.763%	$185.8996	$185.90	$185.90	$185.90
Purchase #3	$110.98	13.841%	$126.3407	$126.34	$126.35	$126.30
Purchase #4	$10.69	6.822%	$11.4193	$11.42	$11.40	$11.40
Purchase #5	$196.56	12.317%	$220.7703	$220.77	$220.75	$220.80
Purchase #6	$177.79	7.358%	$190.8718	$190.87	$190.85	$190.90
Purchase #7	$151.33	9.124%	$165.1373	$165.14	$165.15	$165.10
7 purchase totals =	$836.64		$915.7609	$915.76	$915.70	$915.70