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	$40.47	5.700%	$42.7768	$42.78	$42.80	$42.80
Purchase #2	$111.80	12.767%	$126.0735	$126.07	$126.05	$126.10
Purchase #3	$33.38	5.381%	$35.1762	$35.18	$35.20	$35.20
Purchase #4	$220.51	3.349%	$227.8949	$227.89	$227.90	$227.90
Purchase #5	$137.77	4.533%	$144.0151	$144.02	$144.00	$144.00
Purchase #6	$44.89	6.533%	$47.8227	$47.82	$47.80	$47.80
Purchase #7	$58.99	13.437%	$66.9165	$66.92	$66.90	$66.90
7 purchase totals =	$647.81		$690.6757	$690.68	$690.65	$690.70