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	$19.49	12.325%	$21.8921	$21.89	$21.90	$21.90
Purchase #2	$146.80	13.870%	$167.1612	$167.16	$167.15	$167.20
Purchase #3	$43.46	3.554%	$45.0046	$45.00	$45.00	$45.00
Purchase #4	$243.47	12.859%	$274.7778	$274.78	$274.80	$274.80
Purchase #5	$39.56	10.118%	$43.5627	$43.56	$43.55	$43.60
Purchase #6	$48.56	5.164%	$51.0676	$51.07	$51.05	$51.10
Purchase #7	$145.63	9.584%	$159.5872	$159.59	$159.60	$159.60
7 purchase totals =	$686.97		$763.0532	$763.05	$763.05	$763.20