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 $58.61   13.289%   $66.3987   $66.40   $66.40   $66.40  
  Purchase #2 $103.82   8.822%   $112.979   $112.98   $113.00   $113.00  
  Purchase #3 $149.83   9.372%   $163.8721   $163.87   $163.85   $163.90  
  Purchase #4 $13.84   9.326%   $15.1307   $15.13   $15.15   $15.10  
  Purchase #5 $140.38   10.457%   $155.0595   $155.06   $155.05   $155.10  
  Purchase #6 $89.69   9.193%   $97.9352   $97.94   $97.95   $97.90  
  Purchase #7 $248.77   8.767%   $270.5797   $270.58   $270.60   $270.60  
  7 purchase totals = $804.94       $881.9549   $881.96   $882.00   $882.00