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	$137.33	4.476%	$143.4769	$143.48	$143.50	$143.50
Purchase #2	$102.48	3.519%	$106.0863	$106.09	$106.10	$106.10
Purchase #3	$150.54	13.466%	$170.8117	$170.81	$170.80	$170.80
Purchase #4	$82.28	4.343%	$85.8534	$85.85	$85.85	$85.90
Purchase #5	$88.29	11.261%	$98.2323	$98.23	$98.25	$98.20
Purchase #6	$18.71	10.577%	$20.689	$20.69	$20.70	$20.70
Purchase #7	$216.88	12.407%	$243.7883	$243.79	$243.80	$243.80
7 purchase totals =	$796.51		$868.9379	$868.94	$869.00	$869.00