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	$35.92	8.279%	$38.8938	$38.89	$38.90	$38.90
Purchase #2	$211.87	8.258%	$229.3662	$229.37	$229.35	$229.40
Purchase #3	$32.67	13.807%	$37.1807	$37.18	$37.20	$37.20
Purchase #4	$59.93	3.319%	$61.9191	$61.92	$61.90	$61.90
Purchase #5	$77.90	7.659%	$83.8664	$83.87	$83.85	$83.90
Purchase #6	$103.79	11.789%	$116.0258	$116.03	$116.05	$116.00
Purchase #7	$249.92	6.394%	$265.8999	$265.90	$265.90	$265.90
7 purchase totals =	$772.00		$833.1519	$833.16	$833.15	$833.20