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 $81.66   3.795%   $84.759   $84.76   $84.75   $84.80  
  Purchase #2 $102.96   6.360%   $109.5083   $109.51   $109.50   $109.50  
  Purchase #3 $236.46   12.751%   $266.611   $266.61   $266.60   $266.60  
  Purchase #4 $36.89   13.611%   $41.9111   $41.91   $41.90   $41.90  
  Purchase #5 $146.78   5.744%   $155.211   $155.21   $155.20   $155.20  
  Purchase #6 $179.81   10.200%   $198.1506   $198.15   $198.15   $198.20  
  Purchase #7 $177.80   8.138%   $192.2694   $192.27   $192.25   $192.30  
  7 purchase totals = $962.36       $1,048.4204   $1,048.42   $1,048.35   $1,048.50