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	$153.51	12.186%	$172.2167	$172.22	$172.20	$172.20
Purchase #2	$92.95	12.719%	$104.7723	$104.77	$104.75	$104.80
Purchase #3	$230.87	12.480%	$259.6826	$259.68	$259.70	$259.70
Purchase #4	$248.32	5.475%	$261.9155	$261.92	$261.90	$261.90
Purchase #5	$49.36	8.512%	$53.5615	$53.56	$53.55	$53.60
Purchase #6	$81.87	9.742%	$89.8458	$89.85	$89.85	$89.80
Purchase #7	$185.97	5.398%	$196.0087	$196.01	$196.00	$196.00
7 purchase totals =	$1,042.85		$1,138.0031	$1,138.01	$1,137.95	$1,138.00