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 $88.25   7.546%   $94.9093   $94.91   $94.90   $94.90  
  Purchase #2 $95.83   12.355%   $107.6698   $107.67   $107.65   $107.70  
  Purchase #3 $18.58   13.861%   $21.1554   $21.16   $21.15   $21.20  
  Purchase #4 $26.69   13.356%   $30.2547   $30.25   $30.25   $30.30  
  Purchase #5 $110.33   6.306%   $117.2874   $117.29   $117.30   $117.30  
  Purchase #6 $183.68   3.833%   $190.7205   $190.72   $190.70   $190.70  
  Purchase #7 $241.47   6.612%   $257.436   $257.44   $257.45   $257.40  
  7 purchase totals = $764.83       $819.4331   $819.44   $819.40   $819.50