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	$98.27	13.201%	$111.2426	$111.24	$111.25	$111.20
Purchase #2	$143.78	6.303%	$152.8425	$152.84	$152.85	$152.80
Purchase #3	$32.81	6.735%	$35.0198	$35.02	$35.00	$35.00
Purchase #4	$103.95	12.564%	$117.0103	$117.01	$117.00	$117.00
Purchase #5	$96.89	3.756%	$100.5292	$100.53	$100.55	$100.50
Purchase #6	$239.31	7.726%	$257.7991	$257.80	$257.80	$257.80
Purchase #7	$76.30	11.156%	$84.812	$84.81	$84.80	$84.80
7 purchase totals =	$791.31		$859.2555	$859.25	$859.25	$859.10