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 $53.62   4.370%   $55.9632   $55.96   $55.95   $56.00  
  Purchase #2 $214.63   11.856%   $240.0765   $240.08   $240.10   $240.10  
  Purchase #3 $220.95   9.597%   $242.1546   $242.15   $242.15   $242.20  
  Purchase #4 $44.31   8.354%   $48.0117   $48.01   $48.00   $48.00  
  Purchase #5 $27.54   7.334%   $29.5598   $29.56   $29.55   $29.60  
  Purchase #6 $242.91   4.342%   $253.4572   $253.46   $253.45   $253.50  
  Purchase #7 $178.85   6.257%   $190.0406   $190.04   $190.05   $190.00  
  7 purchase totals = $982.81       $1,059.2636   $1,059.26   $1,059.25   $1,059.40