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	$115.96	13.289%	$131.3699	$131.37	$131.35	$131.40
Purchase #2	$34.28	11.337%	$38.1663	$38.17	$38.15	$38.20
Purchase #3	$143.41	10.300%	$158.1812	$158.18	$158.20	$158.20
Purchase #4	$6.93	13.435%	$7.861	$7.86	$7.85	$7.90
Purchase #5	$80.28	7.327%	$86.1621	$86.16	$86.15	$86.20
Purchase #6	$243.85	11.791%	$272.6024	$272.60	$272.60	$272.60
Purchase #7	$32.80	13.431%	$37.2054	$37.21	$37.20	$37.20
7 purchase totals =	$657.51		$731.5483	$731.55	$731.50	$731.70