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 $155.33   13.764%   $176.7096   $176.71   $176.70   $176.70  
  Purchase #2 $15.43   9.652%   $16.9193   $16.92   $16.90   $16.90  
  Purchase #3 $158.59   10.688%   $175.5401   $175.54   $175.55   $175.50  
  Purchase #4 $77.56   9.336%   $84.801   $84.80   $84.80   $84.80  
  Purchase #5 $82.36   12.859%   $92.9507   $92.95   $92.95   $93.00  
  Purchase #6 $142.47   8.239%   $154.2081   $154.21   $154.20   $154.20  
  Purchase #7 $44.88   13.591%   $50.9796   $50.98   $51.00   $51.00  
  7 purchase totals = $676.62       $752.1084   $752.11   $752.10   $752.10