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 $183.27   6.293%   $194.8032   $194.80   $194.80   $194.80  
  Purchase #2 $102.93   6.618%   $109.7419   $109.74   $109.75   $109.70  
  Purchase #3 $139.97   11.601%   $156.2079   $156.21   $156.20   $156.20  
  Purchase #4 $124.88   3.567%   $129.3345   $129.33   $129.35   $129.30  
  Purchase #5 $69.38   7.647%   $74.6855   $74.69   $74.70   $74.70  
  Purchase #6 $177.25   6.380%   $188.5586   $188.56   $188.55   $188.60  
  Purchase #7 $154.63   11.161%   $171.8883   $171.89   $171.90   $171.90  
  7 purchase totals = $952.31       $1,025.2199   $1,025.22   $1,025.25   $1,025.20