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	$54.31	9.401%	$59.4157	$59.42	$59.40	$59.40
Purchase #2	$22.55	10.696%	$24.9619	$24.96	$24.95	$25.00
Purchase #3	$20.45	12.759%	$23.0592	$23.06	$23.05	$23.10
Purchase #4	$249.34	3.678%	$258.5107	$258.51	$258.50	$258.50
Purchase #5	$6.76	5.489%	$7.1311	$7.13	$7.15	$7.10
Purchase #6	$88.32	13.567%	$100.3024	$100.30	$100.30	$100.30
Purchase #7	$63.87	3.559%	$66.1431	$66.14	$66.15	$66.10
7 purchase totals =	$505.60		$539.5241	$539.52	$539.50	$539.50