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	$129.80	7.810%	$139.9374	$139.94	$139.95	$139.90
Purchase #2	$143.61	8.805%	$156.2549	$156.25	$156.25	$156.30
Purchase #3	$49.84	6.354%	$53.0068	$53.01	$53.00	$53.00
Purchase #4	$90.34	10.271%	$99.6188	$99.62	$99.60	$99.60
Purchase #5	$145.64	13.804%	$165.7441	$165.74	$165.75	$165.70
Purchase #6	$44.51	11.364%	$49.5681	$49.57	$49.55	$49.60
Purchase #7	$157.54	9.504%	$172.5126	$172.51	$172.50	$172.50
7 purchase totals =	$761.28		$836.6427	$836.64	$836.60	$836.60