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	$144.93	3.810%	$150.4518	$150.45	$150.45	$150.50
Purchase #2	$165.73	9.591%	$181.6252	$181.63	$181.65	$181.60
Purchase #3	$72.28	8.105%	$78.1383	$78.14	$78.15	$78.10
Purchase #4	$28.41	3.779%	$29.4836	$29.48	$29.50	$29.50
Purchase #5	$100.71	12.546%	$113.3451	$113.35	$113.35	$113.30
Purchase #6	$69.33	12.399%	$77.9262	$77.93	$77.95	$77.90
Purchase #7	$31.68	9.468%	$34.6795	$34.68	$34.70	$34.70
7 purchase totals =	$613.07		$665.6497	$665.66	$665.75	$665.60