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 $22.91   6.269%   $24.3462   $24.35   $24.35   $24.30  
  Purchase #2 $173.57   3.439%   $179.5391   $179.54   $179.55   $179.50  
  Purchase #3 $192.90   7.759%   $207.8671   $207.87   $207.85   $207.90  
  Purchase #4 $101.48   6.262%   $107.8347   $107.83   $107.85   $107.80  
  Purchase #5 $247.39   12.442%   $278.1703   $278.17   $278.15   $278.20  
  Purchase #6 $179.26   7.782%   $193.21   $193.21   $193.20   $193.20  
  Purchase #7 $28.81   12.195%   $32.3234   $32.32   $32.30   $32.30  
  7 purchase totals = $946.32       $1,023.2908   $1,023.29   $1,023.25   $1,023.20