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	$127.46	9.695%	$139.8172	$139.82	$139.80	$139.80
Purchase #2	$61.77	3.818%	$64.1284	$64.13	$64.15	$64.10
Purchase #3	$180.59	5.742%	$190.9595	$190.96	$190.95	$191.00
Purchase #4	$112.54	8.489%	$122.0935	$122.09	$122.10	$122.10
Purchase #5	$43.79	9.140%	$47.7924	$47.79	$47.80	$47.80
Purchase #6	$25.82	8.470%	$28.007	$28.01	$28.00	$28.00
Purchase #7	$28.59	11.181%	$31.7866	$31.79	$31.80	$31.80
7 purchase totals =	$580.56		$624.5846	$624.59	$624.60	$624.60