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	$7.49	4.189%	$7.8038	$7.80	$7.80	$7.80
Purchase #2	$143.88	11.340%	$160.196	$160.20	$160.20	$160.20
Purchase #3	$100.83	7.328%	$108.2188	$108.22	$108.20	$108.20
Purchase #4	$65.73	6.427%	$69.9545	$69.95	$69.95	$70.00
Purchase #5	$20.34	7.125%	$21.7892	$21.79	$21.80	$21.80
Purchase #6	$141.55	11.795%	$158.2458	$158.25	$158.25	$158.20
Purchase #7	$129.47	9.457%	$141.714	$141.71	$141.70	$141.70
7 purchase totals =	$609.29		$667.9221	$667.92	$667.90	$667.90