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	$27.31	3.637%	$28.3033	$28.30	$28.30	$28.30
Purchase #2	$93.36	8.513%	$101.3077	$101.31	$101.30	$101.30
Purchase #3	$201.72	11.761%	$225.4443	$225.44	$225.45	$225.40
Purchase #4	$184.37	3.527%	$190.8727	$190.87	$190.85	$190.90
Purchase #5	$216.36	4.132%	$225.3	$225.30	$225.30	$225.30
Purchase #6	$66.86	8.836%	$72.7677	$72.77	$72.75	$72.80
Purchase #7	$60.31	10.627%	$66.7191	$66.72	$66.70	$66.70
7 purchase totals =	$850.29		$910.7148	$910.71	$910.65	$910.70