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 $207.48   13.271%   $235.0147   $235.01   $235.00   $235.00  
  Purchase #2 $50.73   9.849%   $55.7264   $55.73   $55.75   $55.70  
  Purchase #3 $135.70   9.494%   $148.5834   $148.58   $148.60   $148.60  
  Purchase #4 $119.57   8.334%   $129.535   $129.54   $129.55   $129.50  
  Purchase #5 $193.25   4.216%   $201.3974   $201.40   $201.40   $201.40  
  Purchase #6 $142.64   4.829%   $149.5281   $149.53   $149.55   $149.50  
  Purchase #7 $243.88   12.624%   $274.6674   $274.67   $274.65   $274.70  
  7 purchase totals = $1,093.25       $1,194.4524   $1,194.46   $1,194.50   $1,194.40