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	$172.90	10.499%	$191.0528	$191.05	$191.05	$191.10
Purchase #2	$140.89	8.153%	$152.3768	$152.38	$152.40	$152.40
Purchase #3	$217.48	9.725%	$238.6299	$238.63	$238.65	$238.60
Purchase #4	$127.90	10.709%	$141.5968	$141.60	$141.60	$141.60
Purchase #5	$209.88	9.696%	$230.23	$230.23	$230.25	$230.20
Purchase #6	$161.51	4.336%	$168.5131	$168.51	$168.50	$168.50
Purchase #7	$86.34	13.282%	$97.8077	$97.81	$97.80	$97.80
7 purchase totals =	$1,116.90		$1,220.2071	$1,220.21	$1,220.25	$1,220.20