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	$89.83	10.778%	$99.5119	$99.51	$99.50	$99.50
Purchase #2	$55.78	10.330%	$61.5421	$61.54	$61.55	$61.50
Purchase #3	$91.82	6.271%	$97.578	$97.58	$97.60	$97.60
Purchase #4	$119.93	3.319%	$123.9105	$123.91	$123.90	$123.90
Purchase #5	$95.60	6.301%	$101.6238	$101.62	$101.60	$101.60
Purchase #6	$94.57	3.131%	$97.531	$97.53	$97.55	$97.50
Purchase #7	$69.48	8.213%	$75.1864	$75.19	$75.20	$75.20
7 purchase totals =	$617.01		$656.8837	$656.88	$656.90	$656.80