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	$112.41	7.480%	$120.8183	$120.82	$120.80	$120.80
Purchase #2	$170.83	11.176%	$189.922	$189.92	$189.90	$189.90
Purchase #3	$122.29	7.242%	$131.1462	$131.15	$131.15	$131.10
Purchase #4	$209.83	13.691%	$238.5578	$238.56	$238.55	$238.60
Purchase #5	$225.82	10.767%	$250.134	$250.13	$250.15	$250.10
Purchase #6	$42.47	6.461%	$45.214	$45.21	$45.20	$45.20
Purchase #7	$19.39	8.752%	$21.087	$21.09	$21.10	$21.10
7 purchase totals =	$903.04		$996.8793	$996.88	$996.85	$996.80