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	$20.61	5.512%	$21.746	$21.75	$21.75	$21.70
Purchase #2	$57.74	3.610%	$59.8244	$59.82	$59.80	$59.80
Purchase #3	$34.97	11.676%	$39.0531	$39.05	$39.05	$39.10
Purchase #4	$72.38	3.691%	$75.0515	$75.05	$75.05	$75.10
Purchase #5	$219.89	13.757%	$250.1403	$250.14	$250.15	$250.10
Purchase #6	$73.42	4.184%	$76.4919	$76.49	$76.50	$76.50
Purchase #7	$17.69	10.398%	$19.5294	$19.53	$19.55	$19.50
7 purchase totals =	$496.70		$541.8366	$541.83	$541.85	$541.80