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 $229.66   13.651%   $261.0109   $261.01   $261.00   $261.00  
  Purchase #2 $248.55   11.219%   $276.4348   $276.43   $276.45   $276.40  
  Purchase #3 $35.68   3.870%   $37.0608   $37.06   $37.05   $37.10  
  Purchase #4 $149.51   13.142%   $169.1586   $169.16   $169.15   $169.20  
  Purchase #5 $174.38   5.122%   $183.3117   $183.31   $183.30   $183.30  
  Purchase #6 $93.64   11.289%   $104.211   $104.21   $104.20   $104.20  
  Purchase #7 $15.65   4.257%   $16.3162   $16.32   $16.30   $16.30  
  7 purchase totals = $947.07       $1,047.5040   $1,047.50   $1,047.45   $1,047.50