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 $57.88   12.474%   $65.1   $65.10   $65.10   $65.10  
  Purchase #2 $114.95   6.471%   $122.3884   $122.39   $122.40   $122.40  
  Purchase #3 $157.66   10.361%   $173.9952   $174.00   $174.00   $174.00  
  Purchase #4 $224.76   7.731%   $242.1362   $242.14   $242.15   $242.10  
  Purchase #5 $32.73   7.248%   $35.1023   $35.10   $35.10   $35.10  
  Purchase #6 $233.38   8.479%   $253.1683   $253.17   $253.15   $253.20  
  Purchase #7 $114.27   6.266%   $121.4302   $121.43   $121.45   $121.40  
  7 purchase totals = $935.63       $1,013.3206   $1,013.33   $1,013.35   $1,013.30