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 $124.96   8.806%   $135.964   $135.96   $135.95   $136.00  
  Purchase #2 $77.61   7.645%   $83.5433   $83.54   $83.55   $83.50  
  Purchase #3 $238.55   7.790%   $257.133   $257.13   $257.15   $257.10  
  Purchase #4 $56.54   13.233%   $64.0219   $64.02   $64.00   $64.00  
  Purchase #5 $133.89   10.710%   $148.2296   $148.23   $148.25   $148.20  
  Purchase #6 $118.99   5.317%   $125.3167   $125.32   $125.30   $125.30  
  Purchase #7 $106.53   13.510%   $120.9222   $120.92   $120.90   $120.90  
  7 purchase totals = $857.07       $935.1307   $935.12   $935.10   $935.00