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	$242.80	5.778%	$256.829	$256.83	$256.85	$256.80
Purchase #2	$83.81	4.227%	$87.3526	$87.35	$87.35	$87.40
Purchase #3	$94.27	6.774%	$100.6558	$100.66	$100.65	$100.70
Purchase #4	$11.86	5.193%	$12.4759	$12.48	$12.50	$12.50
Purchase #5	$33.92	6.530%	$36.135	$36.14	$36.15	$36.10
Purchase #6	$35.67	5.322%	$37.5684	$37.57	$37.55	$37.60
Purchase #7	$107.62	9.171%	$117.4898	$117.49	$117.50	$117.50
7 purchase totals =	$609.95		$648.5065	$648.52	$648.55	$648.60