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	$87.97	13.575%	$99.9119	$99.91	$99.90	$99.90
Purchase #2	$12.29	10.294%	$13.5551	$13.56	$13.55	$13.60
Purchase #3	$188.73	12.805%	$212.8969	$212.90	$212.90	$212.90
Purchase #4	$87.99	4.431%	$91.8888	$91.89	$91.90	$91.90
Purchase #5	$155.98	4.243%	$162.5982	$162.60	$162.60	$162.60
Purchase #6	$175.60	8.796%	$191.0458	$191.05	$191.05	$191.00
Purchase #7	$32.93	8.577%	$35.7544	$35.75	$35.75	$35.80
7 purchase totals =	$741.49		$807.6511	$807.66	$807.65	$807.70