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	$99.82	11.572%	$111.3712	$111.37	$111.35	$111.40
Purchase #2	$133.61	12.354%	$150.1162	$150.12	$150.10	$150.10
Purchase #3	$33.80	9.170%	$36.8995	$36.90	$36.90	$36.90
Purchase #4	$129.96	7.514%	$139.7252	$139.73	$139.75	$139.70
Purchase #5	$13.26	3.480%	$13.7214	$13.72	$13.70	$13.70
Purchase #6	$167.79	4.619%	$175.5402	$175.54	$175.55	$175.50
Purchase #7	$39.64	11.121%	$44.0484	$44.05	$44.05	$44.00
7 purchase totals =	$617.88		$671.4221	$671.43	$671.40	$671.30