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	$37.87	13.330%	$42.9181	$42.92	$42.90	$42.90
Purchase #2	$118.63	6.323%	$126.131	$126.13	$126.15	$126.10
Purchase #3	$5.28	3.542%	$5.467	$5.47	$5.45	$5.50
Purchase #4	$37.89	7.633%	$40.7821	$40.78	$40.80	$40.80
Purchase #5	$32.48	10.582%	$35.917	$35.92	$35.90	$35.90
Purchase #6	$246.42	11.484%	$274.7189	$274.72	$274.70	$274.70
Purchase #7	$228.99	5.320%	$241.1723	$241.17	$241.15	$241.20
7 purchase totals =	$707.56		$767.1064	$767.11	$767.05	$767.10