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	$64.52	10.797%	$71.4862	$71.49	$71.50	$71.50
Purchase #2	$188.53	13.690%	$214.3398	$214.34	$214.35	$214.30
Purchase #3	$10.67	12.363%	$11.9891	$11.99	$12.00	$12.00
Purchase #4	$105.52	5.534%	$111.3595	$111.36	$111.35	$111.40
Purchase #5	$119.54	11.272%	$133.0145	$133.01	$133.00	$133.00
Purchase #6	$168.49	13.449%	$191.1502	$191.15	$191.15	$191.20
Purchase #7	$31.34	12.683%	$35.3149	$35.31	$35.30	$35.30
7 purchase totals =	$688.61		$768.6542	$768.65	$768.65	$768.70