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	$123.47	11.638%	$137.8394	$137.84	$137.85	$137.80
Purchase #2	$232.86	13.426%	$264.1238	$264.12	$264.10	$264.10
Purchase #3	$116.34	6.449%	$123.8428	$123.84	$123.85	$123.80
Purchase #4	$191.78	10.734%	$212.3657	$212.37	$212.35	$212.40
Purchase #5	$179.42	3.134%	$185.043	$185.04	$185.05	$185.00
Purchase #6	$62.39	9.320%	$68.2047	$68.20	$68.20	$68.20
Purchase #7	$40.58	9.599%	$44.4753	$44.48	$44.50	$44.50
7 purchase totals =	$946.84		$1,035.8947	$1,035.89	$1,035.90	$1,035.80