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 $118.63   5.106%   $124.6872   $124.69   $124.70   $124.70  
  Purchase #2 $248.41   4.361%   $259.2432   $259.24   $259.25   $259.20  
  Purchase #3 $67.30   5.516%   $71.0123   $71.01   $71.00   $71.00  
  Purchase #4 $58.90   13.671%   $66.9522   $66.95   $66.95   $67.00  
  Purchase #5 $182.98   6.510%   $194.892   $194.89   $194.90   $194.90  
  Purchase #6 $37.55   6.498%   $39.99   $39.99   $40.00   $40.00  
  Purchase #7 $179.96   10.510%   $198.8738   $198.87   $198.85   $198.90  
  7 purchase totals = $893.73       $955.6507   $955.64   $955.65   $955.70