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	$39.54	8.228%	$42.7934	$42.79	$42.80	$42.80
Purchase #2	$38.25	5.381%	$40.3082	$40.31	$40.30	$40.30
Purchase #3	$240.57	11.750%	$268.837	$268.84	$268.85	$268.80
Purchase #4	$38.47	5.332%	$40.5212	$40.52	$40.50	$40.50
Purchase #5	$9.82	9.287%	$10.732	$10.73	$10.75	$10.70
Purchase #6	$184.79	10.147%	$203.5406	$203.54	$203.55	$203.50
Purchase #7	$151.58	13.507%	$172.0539	$172.05	$172.05	$172.10
7 purchase totals =	$703.02		$778.7863	$778.78	$778.80	$778.70