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	$73.26	10.593%	$81.0204	$81.02	$81.00	$81.00
Purchase #2	$60.40	12.485%	$67.9409	$67.94	$67.95	$67.90
Purchase #3	$25.64	10.808%	$28.4112	$28.41	$28.40	$28.40
Purchase #4	$132.34	3.633%	$137.1479	$137.15	$137.15	$137.10
Purchase #5	$225.27	7.410%	$241.9625	$241.96	$241.95	$242.00
Purchase #6	$87.77	7.690%	$94.5195	$94.52	$94.50	$94.50
Purchase #7	$30.83	5.775%	$32.6104	$32.61	$32.60	$32.60
7 purchase totals =	$635.51		$683.6128	$683.61	$683.55	$683.50