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	$18.63	12.129%	$20.8896	$20.89	$20.90	$20.90
Purchase #2	$72.84	11.316%	$81.0826	$81.08	$81.10	$81.10
Purchase #3	$137.89	12.226%	$154.7484	$154.75	$154.75	$154.70
Purchase #4	$59.27	13.163%	$67.0717	$67.07	$67.05	$67.10
Purchase #5	$53.44	7.469%	$57.4314	$57.43	$57.45	$57.40
Purchase #6	$60.38	11.180%	$67.1305	$67.13	$67.15	$67.10
Purchase #7	$93.47	5.476%	$98.5884	$98.59	$98.60	$98.60
7 purchase totals =	$495.92		$546.9426	$546.94	$547.00	$546.90