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 $93.61   4.728%   $98.0359   $98.04   $98.05   $98.00  
  Purchase #2 $121.36   9.791%   $133.2424   $133.24   $133.25   $133.20  
  Purchase #3 $40.95   6.721%   $43.7022   $43.70   $43.70   $43.70  
  Purchase #4 $106.86   10.441%   $118.0173   $118.02   $118.00   $118.00  
  Purchase #5 $75.73   7.820%   $81.6521   $81.65   $81.65   $81.70  
  Purchase #6 $7.78   9.712%   $8.5356   $8.54   $8.55   $8.50  
  Purchase #7 $216.85   8.198%   $234.6274   $234.63   $234.65   $234.60  
  7 purchase totals = $663.14       $717.8129   $717.82   $717.85   $717.70