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	$94.39	6.391%	$100.4225	$100.42	$100.40	$100.40
Purchase #2	$170.68	3.629%	$176.874	$176.87	$176.85	$176.90
Purchase #3	$139.49	7.400%	$149.8123	$149.81	$149.80	$149.80
Purchase #4	$82.40	11.661%	$92.0087	$92.01	$92.00	$92.00
Purchase #5	$75.89	10.469%	$83.8349	$83.83	$83.85	$83.80
Purchase #6	$131.31	11.695%	$146.6667	$146.67	$146.65	$146.70
Purchase #7	$64.68	11.380%	$72.0406	$72.04	$72.05	$72.00
7 purchase totals =	$758.84		$821.6597	$821.65	$821.60	$821.60