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	$15.27	12.191%	$17.1316	$17.13	$17.15	$17.10
Purchase #2	$68.29	10.459%	$75.4325	$75.43	$75.45	$75.40
Purchase #3	$46.47	4.377%	$48.504	$48.50	$48.50	$48.50
Purchase #4	$26.39	11.790%	$29.5014	$29.50	$29.50	$29.50
Purchase #5	$142.62	6.795%	$152.311	$152.31	$152.30	$152.30
Purchase #6	$86.44	6.613%	$92.1563	$92.16	$92.15	$92.20
Purchase #7	$86.76	4.734%	$90.8672	$90.87	$90.85	$90.90
7 purchase totals =	$472.24		$505.9040	$505.90	$505.90	$505.90