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	$248.28	13.313%	$281.3335	$281.33	$281.35	$281.30
Purchase #2	$139.57	7.755%	$150.3937	$150.39	$150.40	$150.40
Purchase #3	$177.86	6.655%	$189.6966	$189.70	$189.70	$189.70
Purchase #4	$19.73	10.231%	$21.7486	$21.75	$21.75	$21.70
Purchase #5	$100.49	5.143%	$105.6582	$105.66	$105.65	$105.70
Purchase #6	$31.41	5.224%	$33.0509	$33.05	$33.05	$33.10
Purchase #7	$155.82	6.532%	$165.9982	$166.00	$166.00	$166.00
7 purchase totals =	$873.16		$947.8797	$947.88	$947.90	$947.90