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	$37.30	13.126%	$42.196	$42.20	$42.20	$42.20
Purchase #2	$181.60	12.421%	$204.1565	$204.16	$204.15	$204.20
Purchase #3	$147.84	11.243%	$164.4617	$164.46	$164.45	$164.50
Purchase #4	$11.96	3.320%	$12.3571	$12.36	$12.35	$12.40
Purchase #5	$155.86	8.205%	$168.6483	$168.65	$168.65	$168.60
Purchase #6	$83.38	8.812%	$90.7274	$90.73	$90.75	$90.70
Purchase #7	$189.31	5.277%	$199.2999	$199.30	$199.30	$199.30
7 purchase totals =	$807.25		$881.8469	$881.86	$881.85	$881.90