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 $24.56   8.749%   $26.7088   $26.71   $26.70   $26.70  
  Purchase #2 $111.68   6.757%   $119.2262   $119.23   $119.25   $119.20  
  Purchase #3 $68.45   13.588%   $77.751   $77.75   $77.75   $77.80  
  Purchase #4 $139.89   8.190%   $151.347   $151.35   $151.35   $151.30  
  Purchase #5 $187.61   12.276%   $210.641   $210.64   $210.65   $210.60  
  Purchase #6 $134.61   10.448%   $148.6741   $148.67   $148.65   $148.70  
  Purchase #7 $201.92   6.872%   $215.7959   $215.80   $215.80   $215.80  
  7 purchase totals = $868.72       $950.1440   $950.15   $950.15   $950.10