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 $14.72   3.209%   $15.1924   $15.19   $15.20   $15.20  
  Purchase #2 $208.90   13.173%   $236.4184   $236.42   $236.40   $236.40  
  Purchase #3 $145.40   6.219%   $154.4424   $154.44   $154.45   $154.40  
  Purchase #4 $64.32   6.294%   $68.3683   $68.37   $68.35   $68.40  
  Purchase #5 $220.62   3.155%   $227.5806   $227.58   $227.60   $227.60  
  Purchase #6 $24.76   13.389%   $28.0751   $28.08   $28.10   $28.10  
  Purchase #7 $44.70   5.569%   $47.1893   $47.19   $47.20   $47.20  
  7 purchase totals = $723.42       $777.2665   $777.27   $777.30   $777.30