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	$57.64	11.778%	$64.4288	$64.43	$64.45	$64.40
Purchase #2	$34.67	8.595%	$37.6499	$37.65	$37.65	$37.60
Purchase #3	$223.34	13.617%	$253.7522	$253.75	$253.75	$253.80
Purchase #4	$38.87	4.167%	$40.4897	$40.49	$40.50	$40.50
Purchase #5	$9.54	9.663%	$10.4619	$10.46	$10.45	$10.50
Purchase #6	$115.79	7.804%	$124.8263	$124.83	$124.85	$124.80
Purchase #7	$58.45	8.521%	$63.4305	$63.43	$63.45	$63.40
7 purchase totals =	$538.30		$595.0393	$595.04	$595.10	$595.00