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 $79.58   5.759%   $84.163   $84.16   $84.15   $84.20  
  Purchase #2 $71.65   5.506%   $75.595   $75.60   $75.60   $75.60  
  Purchase #3 $133.48   3.457%   $138.0944   $138.09   $138.10   $138.10  
  Purchase #4 $204.41   11.734%   $228.3955   $228.40   $228.40   $228.40  
  Purchase #5 $195.70   5.134%   $205.7472   $205.75   $205.75   $205.70  
  Purchase #6 $186.62   10.419%   $206.0639   $206.06   $206.05   $206.10  
  Purchase #7 $74.63   12.838%   $84.211   $84.21   $84.20   $84.20  
  7 purchase totals = $946.07       $1,022.2700   $1,022.27   $1,022.25   $1,022.30