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	$116.59	3.443%	$120.6042	$120.60	$120.60	$120.60
Purchase #2	$150.66	8.854%	$163.9994	$164.00	$164.00	$164.00
Purchase #3	$199.79	12.635%	$225.0335	$225.03	$225.05	$225.00
Purchase #4	$31.82	12.300%	$35.7339	$35.73	$35.75	$35.70
Purchase #5	$138.83	13.550%	$157.6415	$157.64	$157.65	$157.60
Purchase #6	$123.83	11.191%	$137.6878	$137.69	$137.70	$137.70
Purchase #7	$83.26	8.743%	$90.5394	$90.54	$90.55	$90.50
7 purchase totals =	$844.78		$931.2397	$931.23	$931.30	$931.10