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 $16.25   10.527%   $17.9606   $17.96   $17.95   $18.00  
  Purchase #2 $40.30   4.637%   $42.1687   $42.17   $42.15   $42.20  
  Purchase #3 $28.44   12.508%   $31.9973   $32.00   $32.00   $32.00  
  Purchase #4 $170.35   5.375%   $179.5063   $179.51   $179.50   $179.50  
  Purchase #5 $229.66   11.128%   $255.2166   $255.22   $255.20   $255.20  
  Purchase #6 $195.65   10.291%   $215.7843   $215.78   $215.80   $215.80  
  Purchase #7 $103.91   10.662%   $114.9889   $114.99   $115.00   $115.00  
  7 purchase totals = $784.56       $857.6227   $857.63   $857.60   $857.70