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	$131.93	3.324%	$136.3154	$136.32	$136.30	$136.30
Purchase #2	$83.80	10.399%	$92.5144	$92.51	$92.50	$92.50
Purchase #3	$24.45	11.388%	$27.2344	$27.23	$27.25	$27.20
Purchase #4	$70.98	5.131%	$74.622	$74.62	$74.60	$74.60
Purchase #5	$178.25	5.763%	$188.5225	$188.52	$188.50	$188.50
Purchase #6	$66.66	8.506%	$72.3301	$72.33	$72.35	$72.30
Purchase #7	$141.77	12.484%	$159.4686	$159.47	$159.45	$159.50
7 purchase totals =	$697.84		$751.0074	$751.00	$750.95	$750.90