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 $242.66   9.752%   $266.3242   $266.32   $266.30   $266.30  
  Purchase #2 $80.26   8.226%   $86.8622   $86.86   $86.85   $86.90  
  Purchase #3 $15.83   13.829%   $18.0191   $18.02   $18.00   $18.00  
  Purchase #4 $89.42   3.861%   $92.8725   $92.87   $92.85   $92.90  
  Purchase #5 $155.56   8.156%   $168.2475   $168.25   $168.25   $168.20  
  Purchase #6 $241.41   8.745%   $262.5213   $262.52   $262.50   $262.50  
  Purchase #7 $187.75   7.612%   $202.0415   $202.04   $202.05   $202.00  
  7 purchase totals = $1,012.89       $1,096.8883   $1,096.88   $1,096.80   $1,096.80