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	$89.71	11.480%	$100.0087	$100.01	$100.00	$100.00
Purchase #2	$112.48	11.735%	$125.6795	$125.68	$125.70	$125.70
Purchase #3	$227.89	5.676%	$240.825	$240.83	$240.85	$240.80
Purchase #4	$54.55	6.620%	$58.1612	$58.16	$58.15	$58.20
Purchase #5	$157.25	3.567%	$162.8591	$162.86	$162.85	$162.90
Purchase #6	$67.25	11.628%	$75.0698	$75.07	$75.05	$75.10
Purchase #7	$217.50	10.701%	$240.7747	$240.77	$240.75	$240.80
7 purchase totals =	$926.63		$1,003.3780	$1,003.38	$1,003.35	$1,003.50