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	$132.35	6.554%	$141.0242	$141.02	$141.00	$141.00
Purchase #2	$200.31	13.729%	$227.8106	$227.81	$227.80	$227.80
Purchase #3	$79.58	3.512%	$82.3748	$82.37	$82.35	$82.40
Purchase #4	$41.26	11.262%	$45.9067	$45.91	$45.90	$45.90
Purchase #5	$174.41	6.561%	$185.853	$185.85	$185.85	$185.90
Purchase #6	$92.84	7.297%	$99.6145	$99.61	$99.60	$99.60
Purchase #7	$129.60	7.750%	$139.644	$139.64	$139.65	$139.60
7 purchase totals =	$850.35		$922.2278	$922.21	$922.15	$922.20