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 $68.38   10.732%   $75.7185   $75.72   $75.70   $75.70  
  Purchase #2 $117.63   4.419%   $122.8281   $122.83   $122.85   $122.80  
  Purchase #3 $83.99   10.686%   $92.9652   $92.97   $92.95   $93.00  
  Purchase #4 $16.60   3.285%   $17.1453   $17.15   $17.15   $17.10  
  Purchase #5 $92.61   5.840%   $98.0184   $98.02   $98.00   $98.00  
  Purchase #6 $204.95   12.262%   $230.081   $230.08   $230.10   $230.10  
  Purchase #7 $76.89   10.139%   $84.6859   $84.69   $84.70   $84.70  
  7 purchase totals = $661.05       $721.4424   $721.46   $721.45   $721.40