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	$223.76	13.734%	$254.4912	$254.49	$254.50	$254.50
Purchase #2	$147.77	11.462%	$164.7074	$164.71	$164.70	$164.70
Purchase #3	$227.60	10.110%	$250.6104	$250.61	$250.60	$250.60
Purchase #4	$207.40	8.445%	$224.9149	$224.91	$224.90	$224.90
Purchase #5	$219.71	9.647%	$240.9054	$240.91	$240.90	$240.90
Purchase #6	$47.97	5.242%	$50.4846	$50.48	$50.50	$50.50
Purchase #7	$26.57	11.111%	$29.5222	$29.52	$29.50	$29.50
7 purchase totals =	$1,100.78		$1,215.6361	$1,215.63	$1,215.60	$1,215.60