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	$212.70	4.624%	$222.5352	$222.54	$222.55	$222.50
Purchase #2	$131.61	11.329%	$146.5201	$146.52	$146.50	$146.50
Purchase #3	$116.48	4.133%	$121.2941	$121.29	$121.30	$121.30
Purchase #4	$131.34	12.551%	$147.8245	$147.82	$147.80	$147.80
Purchase #5	$206.73	11.118%	$229.7142	$229.71	$229.70	$229.70
Purchase #6	$244.54	9.471%	$267.7004	$267.70	$267.70	$267.70
Purchase #7	$117.43	5.211%	$123.5493	$123.55	$123.55	$123.50
7 purchase totals =	$1,160.83		$1,259.1378	$1,259.13	$1,259.10	$1,259.00