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 $46.56   13.247%   $52.7278   $52.73   $52.75   $52.70  
  Purchase #2 $119.28   6.478%   $127.007   $127.01   $127.00   $127.00  
  Purchase #3 $102.38   6.625%   $109.1627   $109.16   $109.15   $109.20  
  Purchase #4 $198.76   10.563%   $219.755   $219.76   $219.75   $219.80  
  Purchase #5 $248.31   5.368%   $261.6393   $261.64   $261.65   $261.60  
  Purchase #6 $242.54   5.544%   $255.9864   $255.99   $256.00   $256.00  
  Purchase #7 $243.91   12.500%   $274.3988   $274.40   $274.40   $274.40  
  7 purchase totals = $1,201.74       $1,300.6770   $1,300.69   $1,300.70   $1,300.70