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 $231.86   13.722%   $263.6758   $263.68   $263.70   $263.70  
  Purchase #2 $15.67   9.387%   $17.1409   $17.14   $17.15   $17.10  
  Purchase #3 $36.77   3.684%   $38.1246   $38.12   $38.10   $38.10  
  Purchase #4 $232.89   7.257%   $249.7908   $249.79   $249.80   $249.80  
  Purchase #5 $235.39   10.593%   $260.3249   $260.32   $260.30   $260.30  
  Purchase #6 $218.78   9.624%   $239.8354   $239.84   $239.85   $239.80  
  Purchase #7 $180.59   7.120%   $193.448   $193.45   $193.45   $193.40  
  7 purchase totals = $1,151.95       $1,262.3404   $1,262.34   $1,262.35   $1,262.20