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 $236.47   6.396%   $251.5946   $251.59   $251.60   $251.60  
  Purchase #2 $124.61   5.871%   $131.9259   $131.93   $131.95   $131.90  
  Purchase #3 $68.62   12.172%   $76.9724   $76.97   $76.95   $77.00  
  Purchase #4 $220.60   5.141%   $231.941   $231.94   $231.95   $231.90  
  Purchase #5 $239.49   6.851%   $255.8975   $255.90   $255.90   $255.90  
  Purchase #6 $93.81   7.311%   $100.6684   $100.67   $100.65   $100.70  
  Purchase #7 $18.39   12.529%   $20.6941   $20.69   $20.70   $20.70  
  7 purchase totals = $1,001.99       $1,069.6939   $1,069.69   $1,069.70   $1,069.70