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 $188.67   4.754%   $197.6394   $197.64   $197.65   $197.60  
  Purchase #2 $42.44   4.805%   $44.4792   $44.48   $44.50   $44.50  
  Purchase #3 $28.69   5.448%   $30.253   $30.25   $30.25   $30.30  
  Purchase #4 $225.48   3.630%   $233.6649   $233.66   $233.65   $233.70  
  Purchase #5 $155.66   6.160%   $165.2487   $165.25   $165.25   $165.20  
  Purchase #6 $213.98   4.851%   $224.3602   $224.36   $224.35   $224.40  
  Purchase #7 $71.51   13.254%   $80.9879   $80.99   $81.00   $81.00  
  7 purchase totals = $926.43       $976.6333   $976.63   $976.65   $976.70