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	$56.84	11.443%	$63.3442	$63.34	$63.35	$63.30
Purchase #2	$126.81	11.216%	$141.033	$141.03	$141.05	$141.00
Purchase #3	$77.83	7.628%	$83.7669	$83.77	$83.75	$83.80
Purchase #4	$38.48	10.559%	$42.5431	$42.54	$42.55	$42.50
Purchase #5	$60.74	6.814%	$64.8788	$64.88	$64.90	$64.90
Purchase #6	$89.83	4.417%	$93.7978	$93.80	$93.80	$93.80
Purchase #7	$158.96	11.417%	$177.1085	$177.11	$177.10	$177.10
7 purchase totals =	$609.49		$666.4723	$666.47	$666.50	$666.40