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	$152.84	7.831%	$164.8089	$164.81	$164.80	$164.80
Purchase #2	$35.53	12.259%	$39.8856	$39.89	$39.90	$39.90
Purchase #3	$204.29	9.610%	$223.9223	$223.92	$223.90	$223.90
Purchase #4	$81.65	10.195%	$89.9742	$89.97	$89.95	$90.00
Purchase #5	$153.35	10.576%	$169.5683	$169.57	$169.55	$169.60
Purchase #6	$41.32	13.357%	$46.8391	$46.84	$46.85	$46.80
Purchase #7	$137.87	12.105%	$154.5592	$154.56	$154.55	$154.60
7 purchase totals =	$806.85		$889.5576	$889.56	$889.50	$889.60