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	$108.54	13.717%	$123.4284	$123.43	$123.45	$123.40
Purchase #2	$31.61	13.201%	$35.7828	$35.78	$35.80	$35.80
Purchase #3	$136.40	5.308%	$143.6401	$143.64	$143.65	$143.60
Purchase #4	$137.45	6.867%	$146.8887	$146.89	$146.90	$146.90
Purchase #5	$152.90	5.296%	$160.9976	$161.00	$161.00	$161.00
Purchase #6	$214.95	11.569%	$239.8176	$239.82	$239.80	$239.80
Purchase #7	$97.76	13.426%	$110.8853	$110.89	$110.90	$110.90
7 purchase totals =	$879.61		$961.4405	$961.45	$961.50	$961.40