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	$140.84	4.646%	$147.3834	$147.38	$147.40	$147.40
Purchase #2	$199.26	11.750%	$222.6731	$222.67	$222.65	$222.70
Purchase #3	$80.33	13.529%	$91.1978	$91.20	$91.20	$91.20
Purchase #4	$233.72	9.426%	$255.7504	$255.75	$255.75	$255.80
Purchase #5	$17.54	4.149%	$18.2677	$18.27	$18.25	$18.30
Purchase #6	$79.54	8.846%	$86.5761	$86.58	$86.60	$86.60
Purchase #7	$64.80	13.429%	$73.502	$73.50	$73.50	$73.50
7 purchase totals =	$816.03		$895.3505	$895.35	$895.35	$895.50