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 $165.41   10.589%   $182.9253   $182.93   $182.95   $182.90  
  Purchase #2 $41.56   13.321%   $47.0962   $47.10   $47.10   $47.10  
  Purchase #3 $53.64   9.633%   $58.8071   $58.81   $58.80   $58.80  
  Purchase #4 $71.56   13.560%   $81.2635   $81.26   $81.25   $81.30  
  Purchase #5 $22.45   12.859%   $25.3368   $25.34   $25.35   $25.30  
  Purchase #6 $241.36   11.421%   $268.9257   $268.93   $268.95   $268.90  
  Purchase #7 $232.63   12.570%   $261.8716   $261.87   $261.85   $261.90  
  7 purchase totals = $828.61       $926.2262   $926.24   $926.25   $926.20