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	$203.53	9.230%	$222.3158	$222.32	$222.30	$222.30
Purchase #2	$209.85	5.479%	$221.3477	$221.35	$221.35	$221.30
Purchase #3	$128.82	12.283%	$144.643	$144.64	$144.65	$144.60
Purchase #4	$131.41	11.751%	$146.852	$146.85	$146.85	$146.90
Purchase #5	$59.37	5.211%	$62.4638	$62.46	$62.45	$62.50
Purchase #6	$33.57	9.438%	$36.7383	$36.74	$36.75	$36.70
Purchase #7	$66.51	8.123%	$71.9126	$71.91	$71.90	$71.90
7 purchase totals =	$833.06		$906.2732	$906.27	$906.25	$906.20