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 $99.73   10.252%   $109.9543   $109.95   $109.95   $110.00  
  Purchase #2 $88.42   5.379%   $93.1761   $93.18   $93.20   $93.20  
  Purchase #3 $110.45   6.751%   $117.9065   $117.91   $117.90   $117.90  
  Purchase #4 $69.65   13.280%   $78.8995   $78.90   $78.90   $78.90  
  Purchase #5 $221.99   3.146%   $228.9738   $228.97   $228.95   $229.00  
  Purchase #6 $129.41   11.295%   $144.0269   $144.03   $144.05   $144.00  
  Purchase #7 $107.69   11.158%   $119.7061   $119.71   $119.70   $119.70  
  7 purchase totals = $827.34       $892.6432   $892.65   $892.65   $892.70