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	$125.34	6.276%	$133.2063	$133.21	$133.20	$133.20
Purchase #2	$31.95	10.679%	$35.3619	$35.36	$35.35	$35.40
Purchase #3	$59.50	6.278%	$63.2354	$63.24	$63.25	$63.20
Purchase #4	$29.37	13.578%	$33.3579	$33.36	$33.35	$33.40
Purchase #5	$173.62	3.538%	$179.7627	$179.76	$179.75	$179.80
Purchase #6	$52.27	13.737%	$59.4503	$59.45	$59.45	$59.50
Purchase #7	$76.25	12.499%	$85.7805	$85.78	$85.80	$85.80
7 purchase totals =	$548.30		$590.1550	$590.16	$590.15	$590.30