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	$154.56	12.443%	$173.7919	$173.79	$173.80	$173.80
Purchase #2	$174.51	6.842%	$186.45	$186.45	$186.45	$186.50
Purchase #3	$112.88	11.620%	$125.9967	$126.00	$126.00	$126.00
Purchase #4	$108.77	13.840%	$123.8238	$123.82	$123.80	$123.80
Purchase #5	$36.49	9.485%	$39.9511	$39.95	$39.95	$40.00
Purchase #6	$67.57	5.179%	$71.0695	$71.07	$71.05	$71.10
Purchase #7	$140.83	6.761%	$150.3515	$150.35	$150.35	$150.40
7 purchase totals =	$795.61		$871.4345	$871.43	$871.40	$871.60