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 $82.76   13.206%   $93.6893   $93.69   $93.70   $93.70  
  Purchase #2 $56.53   4.220%   $58.9156   $58.92   $58.90   $58.90  
  Purchase #3 $223.30   4.204%   $232.6875   $232.69   $232.70   $232.70  
  Purchase #4 $121.25   11.867%   $135.6387   $135.64   $135.65   $135.60  
  Purchase #5 $134.69   13.127%   $152.3708   $152.37   $152.35   $152.40  
  Purchase #6 $25.34   10.302%   $27.9505   $27.95   $27.95   $28.00  
  Purchase #7 $35.39   9.708%   $38.8257   $38.83   $38.85   $38.80  
  7 purchase totals = $679.26       $740.0781   $740.09   $740.10   $740.10