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	$17.50	5.831%	$18.5204	$18.52	$18.50	$18.50
Purchase #2	$152.82	3.188%	$157.6919	$157.69	$157.70	$157.70
Purchase #3	$159.66	7.774%	$172.072	$172.07	$172.05	$172.10
Purchase #4	$152.34	12.661%	$171.6278	$171.63	$171.65	$171.60
Purchase #5	$171.48	9.738%	$188.1787	$188.18	$188.20	$188.20
Purchase #6	$59.60	11.816%	$66.6423	$66.64	$66.65	$66.60
Purchase #7	$96.94	9.624%	$106.2695	$106.27	$106.25	$106.30
7 purchase totals =	$810.34		$881.0026	$881.00	$881.00	$881.00