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	$147.38	7.542%	$158.4954	$158.50	$158.50	$158.50
Purchase #2	$42.94	6.133%	$45.5735	$45.57	$45.55	$45.60
Purchase #3	$131.47	8.869%	$143.1301	$143.13	$143.15	$143.10
Purchase #4	$125.77	8.785%	$136.8189	$136.82	$136.80	$136.80
Purchase #5	$18.54	11.282%	$20.6317	$20.63	$20.65	$20.60
Purchase #6	$108.60	10.313%	$119.7999	$119.80	$119.80	$119.80
Purchase #7	$176.25	5.436%	$185.831	$185.83	$185.85	$185.80
7 purchase totals =	$750.95		$810.2805	$810.28	$810.30	$810.20