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	$37.31	8.105%	$40.334	$40.33	$40.35	$40.30
Purchase #2	$246.52	3.621%	$255.4465	$255.45	$255.45	$255.40
Purchase #3	$158.56	5.256%	$166.8939	$166.89	$166.90	$166.90
Purchase #4	$89.49	12.192%	$100.4006	$100.40	$100.40	$100.40
Purchase #5	$153.82	12.769%	$173.4613	$173.46	$173.45	$173.50
Purchase #6	$201.56	10.698%	$223.1229	$223.12	$223.10	$223.10
Purchase #7	$239.82	8.369%	$259.8905	$259.89	$259.90	$259.90
7 purchase totals =	$1,127.08		$1,219.5497	$1,219.54	$1,219.55	$1,219.50