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 $85.33   8.432%   $92.525   $92.53   $92.55   $92.50  
  Purchase #2 $119.49   12.273%   $134.155   $134.16   $134.15   $134.20  
  Purchase #3 $224.77   10.298%   $247.9168   $247.92   $247.90   $247.90  
  Purchase #4 $239.60   9.711%   $262.8676   $262.87   $262.85   $262.90  
  Purchase #5 $51.43   7.366%   $55.2183   $55.22   $55.20   $55.20  
  Purchase #6 $66.70   12.775%   $75.2209   $75.22   $75.20   $75.20  
  Purchase #7 $57.58   8.551%   $62.5037   $62.50   $62.50   $62.50  
  7 purchase totals = $844.90       $930.4073   $930.42   $930.35   $930.40