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	$74.26	7.266%	$79.6557	$79.66	$79.65	$79.70
Purchase #2	$61.73	7.824%	$66.5598	$66.56	$66.55	$66.60
Purchase #3	$117.90	4.800%	$123.5592	$123.56	$123.55	$123.60
Purchase #4	$77.95	13.244%	$88.2737	$88.27	$88.25	$88.30
Purchase #5	$83.51	7.210%	$89.5311	$89.53	$89.55	$89.50
Purchase #6	$171.96	12.141%	$192.8377	$192.84	$192.85	$192.80
Purchase #7	$166.50	5.234%	$175.2146	$175.21	$175.20	$175.20
7 purchase totals =	$753.81		$815.6318	$815.63	$815.60	$815.70