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	$152.52	13.283%	$172.7792	$172.78	$172.80	$172.80
Purchase #2	$30.71	5.830%	$32.5004	$32.50	$32.50	$32.50
Purchase #3	$148.42	11.198%	$165.0401	$165.04	$165.05	$165.00
Purchase #4	$67.28	13.467%	$76.3406	$76.34	$76.35	$76.30
Purchase #5	$45.32	12.702%	$51.0765	$51.08	$51.10	$51.10
Purchase #6	$85.74	11.340%	$95.4629	$95.46	$95.45	$95.50
Purchase #7	$210.98	3.749%	$218.8896	$218.89	$218.90	$218.90
7 purchase totals =	$740.97		$812.0893	$812.09	$812.15	$812.10