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	$158.36	6.266%	$168.2828	$168.28	$168.30	$168.30
Purchase #2	$211.63	7.395%	$227.28	$227.28	$227.30	$227.30
Purchase #3	$111.38	10.511%	$123.0872	$123.09	$123.10	$123.10
Purchase #4	$242.34	3.540%	$250.9188	$250.92	$250.90	$250.90
Purchase #5	$28.71	11.169%	$31.9166	$31.92	$31.90	$31.90
Purchase #6	$85.31	12.576%	$96.0386	$96.04	$96.05	$96.00
Purchase #7	$20.79	13.725%	$23.6434	$23.64	$23.65	$23.60
7 purchase totals =	$858.52		$921.1674	$921.17	$921.20	$921.10