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	$186.51	7.549%	$200.5896	$200.59	$200.60	$200.60
Purchase #2	$74.81	11.395%	$83.3346	$83.33	$83.35	$83.30
Purchase #3	$222.85	4.334%	$232.5083	$232.51	$232.50	$232.50
Purchase #4	$30.69	10.841%	$34.0171	$34.02	$34.00	$34.00
Purchase #5	$149.97	11.526%	$167.2555	$167.26	$167.25	$167.30
Purchase #6	$151.35	8.587%	$164.3464	$164.35	$164.35	$164.30
Purchase #7	$179.84	10.273%	$198.315	$198.32	$198.30	$198.30
7 purchase totals =	$996.02		$1,080.3665	$1,080.38	$1,080.35	$1,080.30