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	$32.34	5.778%	$34.2086	$34.21	$34.20	$34.20
Purchase #2	$64.51	3.689%	$66.8898	$66.89	$66.90	$66.90
Purchase #3	$49.74	6.327%	$52.887	$52.89	$52.90	$52.90
Purchase #4	$84.67	6.727%	$90.3658	$90.37	$90.35	$90.40
Purchase #5	$189.82	5.696%	$200.6321	$200.63	$200.65	$200.60
Purchase #6	$131.74	6.400%	$140.1714	$140.17	$140.15	$140.20
Purchase #7	$205.93	9.706%	$225.9176	$225.92	$225.90	$225.90
7 purchase totals =	$758.75		$811.0723	$811.08	$811.05	$811.10