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	$246.67	9.381%	$269.8101	$269.81	$269.80	$269.80
Purchase #2	$20.53	4.513%	$21.4565	$21.46	$21.45	$21.50
Purchase #3	$36.65	9.498%	$40.131	$40.13	$40.15	$40.10
Purchase #4	$124.61	10.332%	$137.4847	$137.48	$137.50	$137.50
Purchase #5	$145.33	10.619%	$160.7626	$160.76	$160.75	$160.80
Purchase #6	$198.68	13.520%	$225.5415	$225.54	$225.55	$225.50
Purchase #7	$94.86	11.435%	$105.7072	$105.71	$105.70	$105.70
7 purchase totals =	$867.33		$960.8936	$960.89	$960.90	$960.90