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	$250.60	7.135%	$268.4803	$268.48	$268.50	$268.50
Purchase #2	$73.82	3.166%	$76.1571	$76.16	$76.15	$76.20
Purchase #3	$122.61	6.703%	$130.8285	$130.83	$130.85	$130.80
Purchase #4	$86.60	4.749%	$90.7126	$90.71	$90.70	$90.70
Purchase #5	$36.58	9.169%	$39.934	$39.93	$39.95	$39.90
Purchase #6	$243.80	4.750%	$255.3805	$255.38	$255.40	$255.40
Purchase #7	$195.40	12.256%	$219.3482	$219.35	$219.35	$219.30
7 purchase totals =	$1,009.41		$1,080.8412	$1,080.84	$1,080.90	$1,080.80