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	$247.95	10.862%	$274.8823	$274.88	$274.90	$274.90
Purchase #2	$50.25	8.175%	$54.3579	$54.36	$54.35	$54.40
Purchase #3	$158.49	7.212%	$169.9203	$169.92	$169.90	$169.90
Purchase #4	$100.57	3.206%	$103.7943	$103.79	$103.80	$103.80
Purchase #5	$63.69	12.249%	$71.4914	$71.49	$71.50	$71.50
Purchase #6	$223.33	13.711%	$253.9508	$253.95	$253.95	$254.00
Purchase #7	$32.33	5.589%	$34.1369	$34.14	$34.15	$34.10
7 purchase totals =	$876.61		$962.5339	$962.53	$962.55	$962.60