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 $151.87   11.351%   $169.1088   $169.11   $169.10   $169.10  
  Purchase #2 $176.30   6.446%   $187.6643   $187.66   $187.65   $187.70  
  Purchase #3 $245.78   11.418%   $273.8432   $273.84   $273.85   $273.80  
  Purchase #4 $104.62   8.525%   $113.5389   $113.54   $113.55   $113.50  
  Purchase #5 $95.62   10.432%   $105.5951   $105.60   $105.60   $105.60  
  Purchase #6 $104.62   8.484%   $113.496   $113.50   $113.50   $113.50  
  Purchase #7 $57.58   6.695%   $61.435   $61.44   $61.45   $61.40  
  7 purchase totals = $936.39       $1,024.6813   $1,024.69   $1,024.70   $1,024.60