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	$18.64	13.465%	$21.1499	$21.15	$21.15	$21.10
Purchase #2	$134.30	12.542%	$151.1439	$151.14	$151.15	$151.10
Purchase #3	$80.90	12.754%	$91.218	$91.22	$91.20	$91.20
Purchase #4	$206.42	8.396%	$223.751	$223.75	$223.75	$223.80
Purchase #5	$113.96	10.527%	$125.9566	$125.96	$125.95	$126.00
Purchase #6	$67.37	7.388%	$72.3473	$72.35	$72.35	$72.30
Purchase #7	$92.75	13.716%	$105.4716	$105.47	$105.45	$105.50
7 purchase totals =	$714.34		$791.0383	$791.04	$791.00	$791.00