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	$172.46	10.118%	$189.9095	$189.91	$189.90	$189.90
Purchase #2	$144.43	9.851%	$158.6578	$158.66	$158.65	$158.70
Purchase #3	$206.78	10.750%	$229.0089	$229.01	$229.00	$229.00
Purchase #4	$38.94	5.411%	$41.047	$41.05	$41.05	$41.00
Purchase #5	$243.54	13.168%	$275.6093	$275.61	$275.60	$275.60
Purchase #6	$36.88	10.490%	$40.7487	$40.75	$40.75	$40.70
Purchase #7	$140.95	5.542%	$148.7614	$148.76	$148.75	$148.80
7 purchase totals =	$983.98		$1,083.7426	$1,083.75	$1,083.70	$1,083.70