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	$29.53	7.384%	$31.7105	$31.71	$31.70	$31.70
Purchase #2	$250.39	12.546%	$281.8039	$281.80	$281.80	$281.80
Purchase #3	$79.99	10.509%	$88.3961	$88.40	$88.40	$88.40
Purchase #4	$85.29	4.570%	$89.1878	$89.19	$89.20	$89.20
Purchase #5	$205.83	10.515%	$227.473	$227.47	$227.45	$227.50
Purchase #6	$224.25	10.256%	$247.2491	$247.25	$247.25	$247.20
Purchase #7	$41.34	4.240%	$43.0928	$43.09	$43.10	$43.10
7 purchase totals =	$916.62		$1,008.9132	$1,008.91	$1,008.90	$1,008.90