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	$88.77	12.716%	$100.058	$100.06	$100.05	$100.10
Purchase #2	$218.61	4.228%	$227.8528	$227.85	$227.85	$227.90
Purchase #3	$81.50	13.204%	$92.2613	$92.26	$92.25	$92.30
Purchase #4	$233.48	13.324%	$264.5889	$264.59	$264.60	$264.60
Purchase #5	$123.34	11.810%	$137.9065	$137.91	$137.90	$137.90
Purchase #6	$232.77	4.459%	$243.1492	$243.15	$243.15	$243.10
Purchase #7	$13.32	13.113%	$15.0667	$15.07	$15.05	$15.10
7 purchase totals =	$991.79		$1,080.8834	$1,080.89	$1,080.85	$1,081.00