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 $247.49   8.304%   $268.0416   $268.04   $268.05   $268.00  
  Purchase #2 $61.69   13.498%   $70.0169   $70.02   $70.00   $70.00  
  Purchase #3 $90.82   10.688%   $100.5268   $100.53   $100.55   $100.50  
  Purchase #4 $213.39   7.719%   $229.8616   $229.86   $229.85   $229.90  
  Purchase #5 $180.55   10.217%   $198.9968   $199.00   $199.00   $199.00  
  Purchase #6 $164.78   13.330%   $186.7452   $186.75   $186.75   $186.70  
  Purchase #7 $56.95   4.751%   $59.6557   $59.66   $59.65   $59.70  
  7 purchase totals = $1,015.67       $1,113.8446   $1,113.86   $1,113.85   $1,113.80