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 $187.55   11.714%   $209.5196   $209.52   $209.50   $209.50  
  Purchase #2 $104.66   7.278%   $112.2772   $112.28   $112.30   $112.30  
  Purchase #3 $68.53   7.195%   $73.4607   $73.46   $73.45   $73.50  
  Purchase #4 $158.66   5.386%   $167.2054   $167.21   $167.20   $167.20  
  Purchase #5 $115.27   5.458%   $121.5614   $121.56   $121.55   $121.60  
  Purchase #6 $169.94   13.605%   $193.0603   $193.06   $193.05   $193.10  
  Purchase #7 $169.78   7.249%   $182.0874   $182.09   $182.10   $182.10  
  7 purchase totals = $974.39       $1,059.1720   $1,059.18   $1,059.15   $1,059.30