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 $235.93   11.262%   $262.5004   $262.50   $262.50   $262.50  
  Purchase #2 $98.40   10.711%   $108.9396   $108.94   $108.95   $108.90  
  Purchase #3 $17.31   7.389%   $18.589   $18.59   $18.60   $18.60  
  Purchase #4 $88.98   5.523%   $93.8944   $93.89   $93.90   $93.90  
  Purchase #5 $92.70   13.708%   $105.4073   $105.41   $105.40   $105.40  
  Purchase #6 $60.94   5.523%   $64.3057   $64.31   $64.30   $64.30  
  Purchase #7 $161.26   6.780%   $172.1934   $172.19   $172.20   $172.20  
  7 purchase totals = $755.52       $825.8298   $825.83   $825.85   $825.80