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 $243.30   6.495%   $259.1023   $259.10   $259.10   $259.10  
  Purchase #2 $136.49   9.574%   $149.5576   $149.56   $149.55   $149.60  
  Purchase #3 $22.40   6.834%   $23.9308   $23.93   $23.95   $23.90  
  Purchase #4 $215.36   4.566%   $225.1933   $225.19   $225.20   $225.20  
  Purchase #5 $65.57   13.515%   $74.4318   $74.43   $74.45   $74.40  
  Purchase #6 $183.76   7.239%   $197.0624   $197.06   $197.05   $197.10  
  Purchase #7 $114.81   4.201%   $119.6332   $119.63   $119.65   $119.60  
  7 purchase totals = $981.69       $1,048.9114   $1,048.90   $1,048.95   $1,048.90