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	$88.88	11.472%	$99.0763	$99.08	$99.10	$99.10
Purchase #2	$203.84	13.584%	$231.5296	$231.53	$231.55	$231.50
Purchase #3	$10.82	5.651%	$11.4314	$11.43	$11.45	$11.40
Purchase #4	$51.97	8.644%	$56.4623	$56.46	$56.45	$56.50
Purchase #5	$77.67	10.637%	$85.9318	$85.93	$85.95	$85.90
Purchase #6	$242.67	8.783%	$263.9837	$263.98	$264.00	$264.00
Purchase #7	$169.33	13.169%	$191.6291	$191.63	$191.65	$191.60
7 purchase totals =	$845.18		$940.0442	$940.04	$940.15	$940.00