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 $67.27   13.818%   $76.5654   $76.57   $76.55   $76.60  
  Purchase #2 $57.74   12.211%   $64.7906   $64.79   $64.80   $64.80  
  Purchase #3 $39.98   8.838%   $43.5134   $43.51   $43.50   $43.50  
  Purchase #4 $149.53   3.566%   $154.8622   $154.86   $154.85   $154.90  
  Purchase #5 $183.71   9.544%   $201.2433   $201.24   $201.25   $201.20  
  Purchase #6 $241.43   6.724%   $257.6638   $257.66   $257.65   $257.70  
  Purchase #7 $200.28   12.412%   $225.1388   $225.14   $225.15   $225.10  
  7 purchase totals = $939.94       $1,023.7775   $1,023.77   $1,023.75   $1,023.80