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	$47.82	6.446%	$50.9025	$50.90	$50.90	$50.90
Purchase #2	$33.66	6.141%	$35.7271	$35.73	$35.75	$35.70
Purchase #3	$68.51	3.739%	$71.0716	$71.07	$71.05	$71.10
Purchase #4	$239.34	13.201%	$270.9353	$270.94	$270.95	$270.90
Purchase #5	$119.50	3.575%	$123.7721	$123.77	$123.75	$123.80
Purchase #6	$101.87	11.160%	$113.2387	$113.24	$113.25	$113.20
Purchase #7	$78.60	6.110%	$83.4025	$83.40	$83.40	$83.40
7 purchase totals =	$689.30		$749.0498	$749.05	$749.05	$749.00