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	$151.67	8.155%	$164.0387	$164.04	$164.05	$164.00
Purchase #2	$250.28	7.576%	$269.2412	$269.24	$269.25	$269.20
Purchase #3	$75.36	3.158%	$77.7399	$77.74	$77.75	$77.70
Purchase #4	$132.96	4.378%	$138.781	$138.78	$138.80	$138.80
Purchase #5	$230.35	5.313%	$242.5885	$242.59	$242.60	$242.60
Purchase #6	$38.90	10.113%	$42.834	$42.83	$42.85	$42.80
Purchase #7	$52.88	12.420%	$59.4477	$59.45	$59.45	$59.40
7 purchase totals =	$932.40		$994.6710	$994.67	$994.75	$994.50