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	$225.57	13.415%	$255.8302	$255.83	$255.85	$255.80
Purchase #2	$213.71	4.133%	$222.5426	$222.54	$222.55	$222.50
Purchase #3	$247.29	5.698%	$261.3806	$261.38	$261.40	$261.40
Purchase #4	$222.66	12.744%	$251.0358	$251.04	$251.05	$251.00
Purchase #5	$123.53	3.115%	$127.378	$127.38	$127.40	$127.40
Purchase #6	$139.32	6.740%	$148.7102	$148.71	$148.70	$148.70
Purchase #7	$61.49	8.861%	$66.9386	$66.94	$66.95	$66.90
7 purchase totals =	$1,233.57		$1,333.8160	$1,333.82	$1,333.90	$1,333.70