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 $238.73   5.581%   $252.0535   $252.05   $252.05   $252.10  
  Purchase #2 $48.41   5.745%   $51.1912   $51.19   $51.20   $51.20  
  Purchase #3 $71.91   6.443%   $76.5432   $76.54   $76.55   $76.50  
  Purchase #4 $246.61   11.121%   $274.0355   $274.04   $274.05   $274.00  
  Purchase #5 $23.46   12.140%   $26.308   $26.31   $26.30   $26.30  
  Purchase #6 $197.50   5.291%   $207.9497   $207.95   $207.95   $207.90  
  Purchase #7 $175.69   3.699%   $182.1888   $182.19   $182.20   $182.20  
  7 purchase totals = $1,002.31       $1,070.2699   $1,070.27   $1,070.30   $1,070.20