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	$217.38	11.566%	$242.5222	$242.52	$242.50	$242.50
Purchase #2	$160.66	5.477%	$169.4593	$169.46	$169.45	$169.50
Purchase #3	$93.51	13.232%	$105.8832	$105.88	$105.90	$105.90
Purchase #4	$30.44	12.350%	$34.1993	$34.20	$34.20	$34.20
Purchase #5	$159.51	13.629%	$181.2496	$181.25	$181.25	$181.20
Purchase #6	$162.91	7.820%	$175.6496	$175.65	$175.65	$175.60
Purchase #7	$37.76	7.314%	$40.5218	$40.52	$40.50	$40.50
7 purchase totals =	$862.17		$949.4850	$949.48	$949.45	$949.40