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 $104.27   3.219%   $107.6265   $107.63   $107.65   $107.60  
  Purchase #2 $245.26   7.233%   $262.9997   $263.00   $263.00   $263.00  
  Purchase #3 $23.94   11.361%   $26.6598   $26.66   $26.65   $26.70  
  Purchase #4 $14.44   7.609%   $15.5387   $15.54   $15.55   $15.50  
  Purchase #5 $98.32   6.515%   $104.7255   $104.73   $104.75   $104.70  
  Purchase #6 $221.81   8.627%   $240.9455   $240.95   $240.95   $240.90  
  Purchase #7 $231.70   12.648%   $261.0054   $261.01   $261.00   $261.00  
  7 purchase totals = $939.74       $1,019.5011   $1,019.52   $1,019.55   $1,019.40