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	$38.47	11.108%	$42.7432	$42.74	$42.75	$42.70
Purchase #2	$193.35	3.823%	$200.7418	$200.74	$200.75	$200.70
Purchase #3	$76.67	6.289%	$81.4918	$81.49	$81.50	$81.50
Purchase #4	$85.54	3.149%	$88.2337	$88.23	$88.25	$88.20
Purchase #5	$33.82	10.816%	$37.478	$37.48	$37.50	$37.50
Purchase #6	$12.36	13.414%	$14.018	$14.02	$14.00	$14.00
Purchase #7	$22.81	12.218%	$25.5969	$25.60	$25.60	$25.60
7 purchase totals =	$463.02		$490.3034	$490.30	$490.35	$490.20