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 $59.68   9.382%   $65.2792   $65.28   $65.30   $65.30  
  Purchase #2 $204.51   3.401%   $211.4654   $211.47   $211.45   $211.50  
  Purchase #3 $116.47   8.809%   $126.7298   $126.73   $126.75   $126.70  
  Purchase #4 $157.94   13.156%   $178.7186   $178.72   $178.70   $178.70  
  Purchase #5 $5.37   10.414%   $5.9292   $5.93   $5.95   $5.90  
  Purchase #6 $127.37   9.459%   $139.4179   $139.42   $139.40   $139.40  
  Purchase #7 $228.71   3.148%   $235.9098   $235.91   $235.90   $235.90  
  7 purchase totals = $900.05       $963.4499   $963.46   $963.45   $963.40