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 $24.61   7.624%   $26.4863   $26.49   $26.50   $26.50  
  Purchase #2 $238.79   8.678%   $259.5122   $259.51   $259.50   $259.50  
  Purchase #3 $61.35   7.828%   $66.1525   $66.15   $66.15   $66.20  
  Purchase #4 $109.33   8.746%   $118.892   $118.89   $118.90   $118.90  
  Purchase #5 $175.49   6.378%   $186.6828   $186.68   $186.70   $186.70  
  Purchase #6 $22.84   12.734%   $25.7484   $25.75   $25.75   $25.70  
  Purchase #7 $63.59   8.480%   $68.9824   $68.98   $69.00   $69.00  
  7 purchase totals = $696.00       $752.4566   $752.45   $752.50   $752.50