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 $191.84   8.744%   $208.6145   $208.61   $208.60   $208.60  
  Purchase #2 $52.71   13.616%   $59.887   $59.89   $59.90   $59.90  
  Purchase #3 $143.64   11.855%   $160.6685   $160.67   $160.65   $160.70  
  Purchase #4 $47.26   4.714%   $49.4878   $49.49   $49.50   $49.50  
  Purchase #5 $133.69   6.189%   $141.9641   $141.96   $141.95   $142.00  
  Purchase #6 $232.47   12.501%   $261.5311   $261.53   $261.55   $261.50  
  Purchase #7 $214.96   10.243%   $236.9784   $236.98   $237.00   $237.00  
  7 purchase totals = $1,016.57       $1,119.1314   $1,119.13   $1,119.15   $1,119.20