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	$102.66	5.352%	$108.1544	$108.15	$108.15	$108.20
Purchase #2	$56.53	7.215%	$60.6086	$60.61	$60.60	$60.60
Purchase #3	$123.45	11.671%	$137.8578	$137.86	$137.85	$137.90
Purchase #4	$178.83	12.427%	$201.0532	$201.05	$201.05	$201.10
Purchase #5	$230.62	10.577%	$255.0127	$255.01	$255.00	$255.00
Purchase #6	$40.61	11.666%	$45.3476	$45.35	$45.35	$45.30
Purchase #7	$168.42	11.785%	$188.2683	$188.27	$188.25	$188.30
7 purchase totals =	$901.12		$996.3026	$996.30	$996.25	$996.40