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	$121.43	13.260%	$137.5316	$137.53	$137.55	$137.50
Purchase #2	$67.88	3.342%	$70.1485	$70.15	$70.15	$70.10
Purchase #3	$61.85	6.733%	$66.0144	$66.01	$66.00	$66.00
Purchase #4	$209.50	4.695%	$219.336	$219.34	$219.35	$219.30
Purchase #5	$137.89	10.610%	$152.5201	$152.52	$152.50	$152.50
Purchase #6	$175.60	6.746%	$187.446	$187.45	$187.45	$187.40
Purchase #7	$22.46	13.227%	$25.4308	$25.43	$25.45	$25.40
7 purchase totals =	$796.61		$858.4274	$858.43	$858.45	$858.20