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	$23.53	4.138%	$24.5037	$24.50	$24.50	$24.50
Purchase #2	$31.39	7.671%	$33.7979	$33.80	$33.80	$33.80
Purchase #3	$21.90	11.864%	$24.4982	$24.50	$24.50	$24.50
Purchase #4	$81.31	12.594%	$91.5502	$91.55	$91.55	$91.60
Purchase #5	$89.72	11.500%	$100.0378	$100.04	$100.05	$100.00
Purchase #6	$111.54	8.478%	$120.9964	$121.00	$121.00	$121.00
Purchase #7	$218.50	4.717%	$228.8066	$228.81	$228.80	$228.80
7 purchase totals =	$577.89		$624.1908	$624.20	$624.20	$624.20