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	$38.90	11.754%	$43.4723	$43.47	$43.45	$43.50
Purchase #2	$30.41	13.272%	$34.446	$34.45	$34.45	$34.40
Purchase #3	$22.85	4.687%	$23.921	$23.92	$23.90	$23.90
Purchase #4	$57.43	11.865%	$64.2441	$64.24	$64.25	$64.20
Purchase #5	$78.93	10.734%	$87.4023	$87.40	$87.40	$87.40
Purchase #6	$57.74	3.560%	$59.7955	$59.80	$59.80	$59.80
Purchase #7	$180.54	10.352%	$199.2295	$199.23	$199.25	$199.20
7 purchase totals =	$466.80		$512.5107	$512.51	$512.50	$512.40