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	$75.93	10.490%	$83.8951	$83.90	$83.90	$83.90
Purchase #2	$207.34	10.654%	$229.43	$229.43	$229.45	$229.40
Purchase #3	$204.26	6.723%	$217.9924	$217.99	$218.00	$218.00
Purchase #4	$85.66	4.122%	$89.1909	$89.19	$89.20	$89.20
Purchase #5	$230.91	10.659%	$255.5227	$255.52	$255.50	$255.50
Purchase #6	$79.82	5.187%	$83.9603	$83.96	$83.95	$84.00
Purchase #7	$37.47	13.381%	$42.4839	$42.48	$42.50	$42.50
7 purchase totals =	$921.39		$1,002.4753	$1,002.47	$1,002.50	$1,002.50