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 $152.44   12.794%   $171.9432   $171.94   $171.95   $171.90  
  Purchase #2 $196.37   7.580%   $211.2548   $211.25   $211.25   $211.30  
  Purchase #3 $18.98   6.217%   $20.16   $20.16   $20.15   $20.20  
  Purchase #4 $190.72   7.602%   $205.2185   $205.22   $205.20   $205.20  
  Purchase #5 $73.81   10.294%   $81.408   $81.41   $81.40   $81.40  
  Purchase #6 $159.68   6.271%   $169.6935   $169.69   $169.70   $169.70  
  Purchase #7 $191.27   8.571%   $207.6638   $207.66   $207.65   $207.70  
  7 purchase totals = $983.27       $1,067.3418   $1,067.33   $1,067.30   $1,067.40