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 $245.70   6.774%   $262.3437   $262.34   $262.35   $262.30  
  Purchase #2 $184.70   12.462%   $207.7173   $207.72   $207.70   $207.70  
  Purchase #3 $212.87   8.691%   $231.3705   $231.37   $231.35   $231.40  
  Purchase #4 $148.61   5.832%   $157.2769   $157.28   $157.30   $157.30  
  Purchase #5 $177.90   11.672%   $198.6645   $198.66   $198.65   $198.70  
  Purchase #6 $41.46   10.500%   $45.8133   $45.81   $45.80   $45.80  
  Purchase #7 $238.75   7.472%   $256.5894   $256.59   $256.60   $256.60  
  7 purchase totals = $1,249.99       $1,359.7756   $1,359.77   $1,359.75   $1,359.80