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	$230.55	12.435%	$259.2189	$259.22	$259.20	$259.20
Purchase #2	$6.74	11.725%	$7.5303	$7.53	$7.55	$7.50
Purchase #3	$157.52	11.547%	$175.7088	$175.71	$175.70	$175.70
Purchase #4	$37.34	12.209%	$41.8988	$41.90	$41.90	$41.90
Purchase #5	$82.53	7.145%	$88.4268	$88.43	$88.45	$88.40
Purchase #6	$46.46	3.795%	$48.2232	$48.22	$48.20	$48.20
Purchase #7	$67.69	7.416%	$72.7099	$72.71	$72.70	$72.70
7 purchase totals =	$628.83		$693.7167	$693.72	$693.70	$693.60