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 $214.26   9.569%   $234.7625   $234.76   $234.75   $234.80  
  Purchase #2 $121.71   11.777%   $136.0438   $136.04   $136.05   $136.00  
  Purchase #3 $21.67   12.445%   $24.3668   $24.37   $24.35   $24.40  
  Purchase #4 $64.70   9.683%   $70.9649   $70.96   $70.95   $71.00  
  Purchase #5 $248.69   5.139%   $261.4702   $261.47   $261.45   $261.50  
  Purchase #6 $167.58   11.598%   $187.0159   $187.02   $187.00   $187.00  
  Purchase #7 $41.83   11.870%   $46.7952   $46.80   $46.80   $46.80  
  7 purchase totals = $880.44       $961.4193   $961.42   $961.35   $961.50