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 $86.56   12.363%   $97.2614   $97.26   $97.25   $97.30  
  Purchase #2 $14.80   11.148%   $16.4499   $16.45   $16.45   $16.40  
  Purchase #3 $34.44   12.413%   $38.715   $38.72   $38.70   $38.70  
  Purchase #4 $181.75   11.134%   $201.986   $201.99   $202.00   $202.00  
  Purchase #5 $164.71   12.546%   $185.3745   $185.37   $185.35   $185.40  
  Purchase #6 $126.70   10.745%   $140.3139   $140.31   $140.30   $140.30  
  Purchase #7 $218.67   3.220%   $225.7112   $225.71   $225.70   $225.70  
  7 purchase totals = $827.63       $905.8119   $905.81   $905.75   $905.80