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 $119.34   4.292%   $124.4621   $124.46   $124.45   $124.50  
  Purchase #2 $181.49   9.549%   $198.8205   $198.82   $198.80   $198.80  
  Purchase #3 $216.54   3.850%   $224.8768   $224.88   $224.90   $224.90  
  Purchase #4 $82.82   12.818%   $93.4359   $93.44   $93.45   $93.40  
  Purchase #5 $85.69   10.118%   $94.3601   $94.36   $94.35   $94.40  
  Purchase #6 $26.98   6.315%   $28.6838   $28.68   $28.70   $28.70  
  Purchase #7 $179.77   11.384%   $200.235   $200.24   $200.25   $200.20  
  7 purchase totals = $892.63       $964.8742   $964.88   $964.90   $964.90