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 $146.70   4.163%   $152.8071   $152.81   $152.80   $152.80  
  Purchase #2 $56.58   5.453%   $59.6653   $59.67   $59.65   $59.70  
  Purchase #3 $60.36   4.795%   $63.2543   $63.25   $63.25   $63.30  
  Purchase #4 $178.87   11.661%   $199.728   $199.73   $199.75   $199.70  
  Purchase #5 $182.86   7.726%   $196.9878   $196.99   $197.00   $197.00  
  Purchase #6 $74.90   8.413%   $81.2013   $81.20   $81.20   $81.20  
  Purchase #7 $89.44   4.638%   $93.5882   $93.59   $93.60   $93.60  
  7 purchase totals = $789.71       $847.2320   $847.24   $847.25   $847.30