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	$99.59	12.289%	$111.8286	$111.83	$111.85	$111.80
Purchase #2	$111.61	8.395%	$120.9797	$120.98	$121.00	$121.00
Purchase #3	$128.32	7.824%	$138.3598	$138.36	$138.35	$138.40
Purchase #4	$53.63	6.359%	$57.0403	$57.04	$57.05	$57.00
Purchase #5	$230.26	12.592%	$259.2543	$259.25	$259.25	$259.30
Purchase #6	$85.78	3.259%	$88.5756	$88.58	$88.60	$88.60
Purchase #7	$135.98	3.528%	$140.7774	$140.78	$140.80	$140.80
7 purchase totals =	$845.17		$916.8157	$916.82	$916.90	$916.90