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	$215.43	5.151%	$226.5268	$226.53	$226.55	$226.50
Purchase #2	$86.69	9.644%	$95.0504	$95.05	$95.05	$95.10
Purchase #3	$127.40	13.285%	$144.3251	$144.33	$144.35	$144.30
Purchase #4	$10.69	8.218%	$11.5685	$11.57	$11.55	$11.60
Purchase #5	$77.82	12.408%	$87.4759	$87.48	$87.50	$87.50
Purchase #6	$146.96	11.748%	$164.2249	$164.22	$164.20	$164.20
Purchase #7	$248.69	10.123%	$273.8649	$273.86	$273.85	$273.90
7 purchase totals =	$913.68		$1,003.0365	$1,003.04	$1,003.05	$1,003.10