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	$37.95	11.646%	$42.3697	$42.37	$42.35	$42.40
Purchase #2	$177.34	13.232%	$200.8056	$200.81	$200.80	$200.80
Purchase #3	$127.40	11.390%	$141.9109	$141.91	$141.90	$141.90
Purchase #4	$68.58	6.776%	$73.227	$73.23	$73.25	$73.20
Purchase #5	$109.96	4.118%	$114.4882	$114.49	$114.50	$114.50
Purchase #6	$176.51	12.865%	$199.218	$199.22	$199.20	$199.20
Purchase #7	$6.80	5.359%	$7.1644	$7.16	$7.15	$7.20
7 purchase totals =	$704.54		$779.1838	$779.19	$779.15	$779.20