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 $174.53   5.208%   $183.6195   $183.62   $183.60   $183.60  
  Purchase #2 $115.77   7.856%   $124.8649   $124.86   $124.85   $124.90  
  Purchase #3 $58.96   6.257%   $62.6491   $62.65   $62.65   $62.60  
  Purchase #4 $131.77   6.469%   $140.2942   $140.29   $140.30   $140.30  
  Purchase #5 $231.43   10.353%   $255.3899   $255.39   $255.40   $255.40  
  Purchase #6 $6.58   5.347%   $6.9318   $6.93   $6.95   $6.90  
  Purchase #7 $242.61   7.544%   $260.9125   $260.91   $260.90   $260.90  
  7 purchase totals = $961.65       $1,034.6619   $1,034.65   $1,034.65   $1,034.60