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	$45.46	6.260%	$48.3058	$48.31	$48.30	$48.30
Purchase #2	$201.49	10.382%	$222.4087	$222.41	$222.40	$222.40
Purchase #3	$185.92	12.511%	$209.1805	$209.18	$209.20	$209.20
Purchase #4	$117.85	12.436%	$132.5058	$132.51	$132.50	$132.50
Purchase #5	$97.71	11.384%	$108.8333	$108.83	$108.85	$108.80
Purchase #6	$172.53	4.310%	$179.966	$179.97	$179.95	$180.00
Purchase #7	$105.69	5.438%	$111.4374	$111.44	$111.45	$111.40
7 purchase totals =	$926.65		$1,012.6375	$1,012.65	$1,012.65	$1,012.60