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 $24.56   8.165%   $26.5653   $26.57   $26.55   $26.60  
  Purchase #2 $188.49   10.786%   $208.8205   $208.82   $208.80   $208.80  
  Purchase #3 $122.62   3.570%   $126.9975   $127.00   $127.00   $127.00  
  Purchase #4 $163.94   12.492%   $184.4194   $184.42   $184.40   $184.40  
  Purchase #5 $103.55   4.775%   $108.4945   $108.49   $108.50   $108.50  
  Purchase #6 $228.45   12.222%   $256.3712   $256.37   $256.35   $256.40  
  Purchase #7 $137.79   12.366%   $154.8291   $154.83   $154.85   $154.80  
  7 purchase totals = $969.40       $1,066.4975   $1,066.50   $1,066.45   $1,066.50