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 $55.55   9.562%   $60.8617   $60.86   $60.85   $60.90  
  Purchase #2 $246.99   8.722%   $268.5325   $268.53   $268.55   $268.50  
  Purchase #3 $62.69   10.336%   $69.1696   $69.17   $69.15   $69.20  
  Purchase #4 $26.89   13.353%   $30.4806   $30.48   $30.50   $30.50  
  Purchase #5 $75.62   13.706%   $85.9845   $85.98   $86.00   $86.00  
  Purchase #6 $40.44   12.264%   $45.3996   $45.40   $45.40   $45.40  
  Purchase #7 $122.92   6.790%   $131.2663   $131.27   $131.25   $131.30  
  7 purchase totals = $631.10       $691.6948   $691.69   $691.70   $691.80