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	$12.66	10.328%	$13.9675	$13.97	$13.95	$14.00
Purchase #2	$240.29	13.234%	$272.09	$272.09	$272.10	$272.10
Purchase #3	$72.53	7.797%	$78.1852	$78.19	$78.20	$78.20
Purchase #4	$155.27	6.339%	$165.1126	$165.11	$165.10	$165.10
Purchase #5	$83.56	7.160%	$89.5429	$89.54	$89.55	$89.50
Purchase #6	$10.37	3.591%	$10.7424	$10.74	$10.75	$10.70
Purchase #7	$32.79	13.277%	$37.1435	$37.14	$37.15	$37.10
7 purchase totals =	$607.47		$666.7841	$666.78	$666.80	$666.70