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	$161.73	11.845%	$180.8869	$180.89	$180.90	$180.90
Purchase #2	$90.41	13.184%	$102.3297	$102.33	$102.35	$102.30
Purchase #3	$133.51	12.505%	$150.2054	$150.21	$150.20	$150.20
Purchase #4	$38.65	6.667%	$41.2268	$41.23	$41.25	$41.20
Purchase #5	$37.71	4.456%	$39.3904	$39.39	$39.40	$39.40
Purchase #6	$70.61	11.707%	$78.8763	$78.88	$78.90	$78.90
Purchase #7	$54.99	8.514%	$59.6718	$59.67	$59.65	$59.70
7 purchase totals =	$587.61		$652.5873	$652.60	$652.65	$652.60