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	$30.53	7.378%	$32.7825	$32.78	$32.80	$32.80
Purchase #2	$92.77	4.815%	$97.2369	$97.24	$97.25	$97.20
Purchase #3	$77.60	10.224%	$85.5338	$85.53	$85.55	$85.50
Purchase #4	$163.54	5.151%	$171.9639	$171.96	$171.95	$172.00
Purchase #5	$82.29	4.438%	$85.942	$85.94	$85.95	$85.90
Purchase #6	$92.90	13.477%	$105.4201	$105.42	$105.40	$105.40
Purchase #7	$38.95	8.761%	$42.3624	$42.36	$42.35	$42.40
7 purchase totals =	$578.58		$621.2416	$621.23	$621.25	$621.20