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	$55.89	7.175%	$59.9001	$59.90	$59.90	$59.90
Purchase #2	$202.87	11.261%	$225.7152	$225.72	$225.70	$225.70
Purchase #3	$217.40	13.232%	$246.1664	$246.17	$246.15	$246.20
Purchase #4	$10.32	5.471%	$10.8846	$10.88	$10.90	$10.90
Purchase #5	$236.66	6.241%	$251.43	$251.43	$251.45	$251.40
Purchase #6	$206.76	13.509%	$234.6912	$234.69	$234.70	$234.70
Purchase #7	$145.44	10.331%	$160.4654	$160.47	$160.45	$160.50
7 purchase totals =	$1,075.34		$1,189.2529	$1,189.26	$1,189.25	$1,189.30