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 $66.37   3.779%   $68.8781   $68.88   $68.90   $68.90  
  Purchase #2 $88.54   9.332%   $96.8026   $96.80   $96.80   $96.80  
  Purchase #3 $109.90   11.566%   $122.611   $122.61   $122.60   $122.60  
  Purchase #4 $111.27   7.772%   $119.9179   $119.92   $119.90   $119.90  
  Purchase #5 $87.49   6.427%   $93.113   $93.11   $93.10   $93.10  
  Purchase #6 $146.89   12.309%   $164.9707   $164.97   $164.95   $165.00  
  Purchase #7 $250.29   3.256%   $258.4394   $258.44   $258.45   $258.40  
  7 purchase totals = $860.75       $924.7327   $924.73   $924.70   $924.70