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	$242.52	8.841%	$263.9612	$263.96	$263.95	$264.00
Purchase #2	$228.34	3.651%	$236.6767	$236.68	$236.70	$236.70
Purchase #3	$140.64	6.256%	$149.4384	$149.44	$149.45	$149.40
Purchase #4	$177.55	10.666%	$196.4875	$196.49	$196.50	$196.50
Purchase #5	$124.37	10.642%	$137.6055	$137.61	$137.60	$137.60
Purchase #6	$75.32	4.487%	$78.6996	$78.70	$78.70	$78.70
Purchase #7	$122.86	12.333%	$138.0123	$138.01	$138.00	$138.00
7 purchase totals =	$1,111.60		$1,200.8812	$1,200.89	$1,200.90	$1,200.90