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	$157.52	6.252%	$167.3682	$167.37	$167.35	$167.40
Purchase #2	$131.62	4.527%	$137.5784	$137.58	$137.60	$137.60
Purchase #3	$59.90	12.677%	$67.4935	$67.49	$67.50	$67.50
Purchase #4	$210.77	6.816%	$225.1361	$225.14	$225.15	$225.10
Purchase #5	$18.80	7.676%	$20.2431	$20.24	$20.25	$20.20
Purchase #6	$137.98	6.440%	$146.8659	$146.87	$146.85	$146.90
Purchase #7	$7.62	3.263%	$7.8686	$7.87	$7.85	$7.90
7 purchase totals =	$724.21		$772.5538	$772.56	$772.55	$772.60