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 $246.53   6.474%   $262.4904   $262.49   $262.50   $262.50  
  Purchase #2 $168.31   13.320%   $190.7289   $190.73   $190.75   $190.70  
  Purchase #3 $26.26   5.756%   $27.7715   $27.77   $27.75   $27.80  
  Purchase #4 $83.99   4.429%   $87.7099   $87.71   $87.70   $87.70  
  Purchase #5 $55.55   3.247%   $57.3537   $57.35   $57.35   $57.40  
  Purchase #6 $78.59   9.660%   $86.1818   $86.18   $86.20   $86.20  
  Purchase #7 $226.27   12.873%   $255.3977   $255.40   $255.40   $255.40  
  7 purchase totals = $885.50       $967.6339   $967.63   $967.65   $967.70