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 $234.86   13.361%   $266.2396   $266.24   $266.25   $266.20  
  Purchase #2 $165.75   10.173%   $182.6117   $182.61   $182.60   $182.60  
  Purchase #3 $143.49   13.713%   $163.1668   $163.17   $163.15   $163.20  
  Purchase #4 $66.38   8.681%   $72.1424   $72.14   $72.15   $72.10  
  Purchase #5 $56.68   12.847%   $63.9617   $63.96   $63.95   $64.00  
  Purchase #6 $246.51   13.511%   $279.816   $279.82   $279.80   $279.80  
  Purchase #7 $78.83   7.275%   $84.5649   $84.56   $84.55   $84.60  
  7 purchase totals = $992.50       $1,112.5031   $1,112.50   $1,112.45   $1,112.50