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	$246.27	7.679%	$265.1811	$265.18	$265.20	$265.20
Purchase #2	$85.39	6.370%	$90.8293	$90.83	$90.85	$90.80
Purchase #3	$243.47	11.248%	$270.8555	$270.86	$270.85	$270.90
Purchase #4	$31.70	6.387%	$33.7247	$33.72	$33.70	$33.70
Purchase #5	$47.49	12.369%	$53.364	$53.36	$53.35	$53.40
Purchase #6	$127.87	7.143%	$137.0038	$137.00	$137.00	$137.00
Purchase #7	$62.43	12.797%	$70.4192	$70.42	$70.40	$70.40
7 purchase totals =	$844.62		$921.3776	$921.37	$921.35	$921.40