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	$175.27	7.486%	$188.3907	$188.39	$188.40	$188.40
Purchase #2	$160.47	13.316%	$181.8382	$181.84	$181.85	$181.80
Purchase #3	$234.96	8.692%	$255.3827	$255.38	$255.40	$255.40
Purchase #4	$97.95	10.603%	$108.3356	$108.34	$108.35	$108.30
Purchase #5	$36.66	11.571%	$40.9019	$40.90	$40.90	$40.90
Purchase #6	$240.85	11.240%	$267.9215	$267.92	$267.90	$267.90
Purchase #7	$6.66	3.843%	$6.9159	$6.92	$6.90	$6.90
7 purchase totals =	$952.82		$1,049.6865	$1,049.69	$1,049.70	$1,049.60