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	$137.75	7.606%	$148.2273	$148.23	$148.25	$148.20
Purchase #2	$112.91	3.466%	$116.8235	$116.82	$116.80	$116.80
Purchase #3	$52.40	13.568%	$59.5096	$59.51	$59.50	$59.50
Purchase #4	$222.81	7.340%	$239.1643	$239.16	$239.15	$239.20
Purchase #5	$149.53	12.129%	$167.6665	$167.67	$167.65	$167.70
Purchase #6	$70.42	10.362%	$77.7169	$77.72	$77.70	$77.70
Purchase #7	$36.90	12.576%	$41.5405	$41.54	$41.55	$41.50
7 purchase totals =	$782.72		$850.6486	$850.65	$850.60	$850.60