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 $56.85   8.124%   $61.4685   $61.47   $61.45   $61.50  
  Purchase #2 $9.60   3.269%   $9.9138   $9.91   $9.90   $9.90  
  Purchase #3 $26.29   6.458%   $27.9878   $27.99   $28.00   $28.00  
  Purchase #4 $110.50   8.285%   $119.6549   $119.65   $119.65   $119.70  
  Purchase #5 $248.71   4.520%   $259.9517   $259.95   $259.95   $260.00  
  Purchase #6 $127.96   4.532%   $133.7591   $133.76   $133.75   $133.80  
  Purchase #7 $216.43   13.417%   $245.4684   $245.47   $245.45   $245.50  
  7 purchase totals = $796.34       $858.2042   $858.20   $858.15   $858.40