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	$36.26	12.401%	$40.7566	$40.76	$40.75	$40.80
Purchase #2	$40.61	9.775%	$44.5796	$44.58	$44.60	$44.60
Purchase #3	$83.78	6.812%	$89.4871	$89.49	$89.50	$89.50
Purchase #4	$126.89	6.214%	$134.7749	$134.77	$134.75	$134.80
Purchase #5	$149.31	10.510%	$165.0025	$165.00	$165.00	$165.00
Purchase #6	$171.86	11.320%	$191.3146	$191.31	$191.30	$191.30
Purchase #7	$71.52	3.392%	$73.946	$73.95	$73.95	$73.90
7 purchase totals =	$680.23		$739.8613	$739.86	$739.85	$739.90