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	$66.89	6.189%	$71.0298	$71.03	$71.05	$71.00
Purchase #2	$62.34	3.732%	$64.6665	$64.67	$64.65	$64.70
Purchase #3	$32.62	8.312%	$35.3314	$35.33	$35.35	$35.30
Purchase #4	$194.78	9.588%	$213.4555	$213.46	$213.45	$213.50
Purchase #5	$28.47	4.709%	$29.8107	$29.81	$29.80	$29.80
Purchase #6	$97.48	11.779%	$108.9622	$108.96	$108.95	$109.00
Purchase #7	$11.31	9.598%	$12.3955	$12.40	$12.40	$12.40
7 purchase totals =	$493.89		$535.6516	$535.66	$535.65	$535.70