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 $94.93   8.648%   $103.1395   $103.14   $103.15   $103.10  
  Purchase #2 $164.94   11.102%   $183.2516   $183.25   $183.25   $183.30  
  Purchase #3 $242.64   10.440%   $267.9716   $267.97   $267.95   $268.00  
  Purchase #4 $54.38   12.120%   $60.9709   $60.97   $60.95   $61.00  
  Purchase #5 $234.49   8.651%   $254.7757   $254.78   $254.80   $254.80  
  Purchase #6 $22.70   10.168%   $25.0081   $25.01   $25.00   $25.00  
  Purchase #7 $234.25   3.526%   $242.5097   $242.51   $242.50   $242.50  
  7 purchase totals = $1,048.33       $1,137.6271   $1,137.63   $1,137.60   $1,137.70