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 $250.63   12.554%   $282.0941   $282.09   $282.10   $282.10  
  Purchase #2 $91.75   5.453%   $96.7531   $96.75   $96.75   $96.80  
  Purchase #3 $104.54   3.118%   $107.7996   $107.80   $107.80   $107.80  
  Purchase #4 $56.89   4.441%   $59.4165   $59.42   $59.40   $59.40  
  Purchase #5 $8.57   7.554%   $9.2174   $9.22   $9.20   $9.20  
  Purchase #6 $58.43   11.644%   $65.2336   $65.23   $65.25   $65.20  
  Purchase #7 $11.34   6.301%   $12.0545   $12.05   $12.05   $12.10  
  7 purchase totals = $582.15       $632.5688   $632.56   $632.55   $632.60