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	$80.50	7.163%	$86.2662	$86.27	$86.25	$86.30
Purchase #2	$10.61	7.721%	$11.4292	$11.43	$11.45	$11.40
Purchase #3	$122.70	13.439%	$139.1897	$139.19	$139.20	$139.20
Purchase #4	$17.32	7.449%	$18.6102	$18.61	$18.60	$18.60
Purchase #5	$72.89	10.167%	$80.3007	$80.30	$80.30	$80.30
Purchase #6	$68.74	13.215%	$77.824	$77.82	$77.80	$77.80
Purchase #7	$37.34	8.626%	$40.5609	$40.56	$40.55	$40.60
7 purchase totals =	$410.10		$454.1809	$454.18	$454.15	$454.20