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 $233.38   12.151%   $261.738   $261.74   $261.75   $261.70  
  Purchase #2 $54.29   12.447%   $61.0475   $61.05   $61.05   $61.00  
  Purchase #3 $214.31   12.263%   $240.5908   $240.59   $240.60   $240.60  
  Purchase #4 $169.29   7.262%   $181.5838   $181.58   $181.60   $181.60  
  Purchase #5 $223.63   5.483%   $235.8916   $235.89   $235.90   $235.90  
  Purchase #6 $152.35   13.639%   $173.129   $173.13   $173.15   $173.10  
  Purchase #7 $201.74   3.595%   $208.9926   $208.99   $209.00   $209.00  
  7 purchase totals = $1,248.99       $1,362.9733   $1,362.97   $1,363.05   $1,362.90