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 $24.45   8.554%   $26.5415   $26.54   $26.55   $26.50  
  Purchase #2 $113.89   9.436%   $124.6367   $124.64   $124.65   $124.60  
  Purchase #3 $72.77   12.679%   $81.9965   $82.00   $82.00   $82.00  
  Purchase #4 $246.75   3.515%   $255.4233   $255.42   $255.40   $255.40  
  Purchase #5 $71.95   11.654%   $80.3351   $80.34   $80.35   $80.30  
  Purchase #6 $102.61   10.175%   $113.0506   $113.05   $113.05   $113.10  
  Purchase #7 $153.55   5.470%   $161.9492   $161.95   $161.95   $161.90  
  7 purchase totals = $785.97       $843.9329   $843.94   $843.95   $843.80