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 $222.49   13.635%   $252.8265   $252.83   $252.85   $252.80  
  Purchase #2 $200.72   9.424%   $219.6359   $219.64   $219.65   $219.60  
  Purchase #3 $168.31   10.449%   $185.8967   $185.90   $185.90   $185.90  
  Purchase #4 $247.29   5.582%   $261.0937   $261.09   $261.10   $261.10  
  Purchase #5 $50.62   9.161%   $55.2573   $55.26   $55.25   $55.30  
  Purchase #6 $236.94   10.259%   $261.2477   $261.25   $261.25   $261.20  
  Purchase #7 $162.40   9.684%   $178.1268   $178.13   $178.15   $178.10  
  7 purchase totals = $1,288.77       $1,414.0846   $1,414.10   $1,414.15   $1,414.00