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	$101.34	5.184%	$106.5935	$106.59	$106.60	$106.60
Purchase #2	$102.54	6.700%	$109.4102	$109.41	$109.40	$109.40
Purchase #3	$185.77	5.778%	$196.5038	$196.50	$196.50	$196.50
Purchase #4	$62.32	7.321%	$66.8824	$66.88	$66.90	$66.90
Purchase #5	$226.60	10.534%	$250.47	$250.47	$250.45	$250.50
Purchase #6	$8.48	7.328%	$9.1014	$9.10	$9.10	$9.10
Purchase #7	$112.87	7.523%	$121.3612	$121.36	$121.35	$121.40
7 purchase totals =	$799.92		$860.3225	$860.31	$860.30	$860.40