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 $43.31   13.610%   $49.2045   $49.20   $49.20   $49.20  
  Purchase #2 $201.26   6.182%   $213.7019   $213.70   $213.70   $213.70  
  Purchase #3 $109.33   7.760%   $117.814   $117.81   $117.80   $117.80  
  Purchase #4 $183.62   7.434%   $197.2703   $197.27   $197.25   $197.30  
  Purchase #5 $153.40   7.484%   $164.8805   $164.88   $164.90   $164.90  
  Purchase #6 $77.33   13.273%   $87.594   $87.59   $87.60   $87.60  
  Purchase #7 $97.51   6.653%   $103.9973   $104.00   $104.00   $104.00  
  7 purchase totals = $865.76       $934.4625   $934.45   $934.45   $934.50