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	$243.43	6.117%	$258.3206	$258.32	$258.30	$258.30
Purchase #2	$70.53	7.192%	$75.6025	$75.60	$75.60	$75.60
Purchase #3	$160.61	12.219%	$180.2349	$180.23	$180.25	$180.20
Purchase #4	$149.54	11.208%	$166.3004	$166.30	$166.30	$166.30
Purchase #5	$141.49	7.358%	$151.9008	$151.90	$151.90	$151.90
Purchase #6	$79.97	13.300%	$90.606	$90.61	$90.60	$90.60
Purchase #7	$44.93	5.644%	$47.4658	$47.47	$47.45	$47.50
7 purchase totals =	$890.50		$970.4310	$970.43	$970.40	$970.40