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 $217.75   13.556%   $247.2682   $247.27   $247.25   $247.30  
  Purchase #2 $102.75   6.429%   $109.3558   $109.36   $109.35   $109.40  
  Purchase #3 $112.58   8.789%   $122.4747   $122.47   $122.45   $122.50  
  Purchase #4 $46.42   12.832%   $52.3766   $52.38   $52.40   $52.40  
  Purchase #5 $49.41   9.105%   $53.9088   $53.91   $53.90   $53.90  
  Purchase #6 $214.44   9.366%   $234.5245   $234.52   $234.50   $234.50  
  Purchase #7 $205.97   13.492%   $233.7595   $233.76   $233.75   $233.80  
  7 purchase totals = $949.32       $1,053.6681   $1,053.67   $1,053.60   $1,053.80