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 $23.92   8.528%   $25.9599   $25.96   $25.95   $26.00  
  Purchase #2 $33.67   6.539%   $35.8717   $35.87   $35.85   $35.90  
  Purchase #3 $55.74   6.696%   $59.4724   $59.47   $59.45   $59.50  
  Purchase #4 $20.74   13.479%   $23.5355   $23.54   $23.55   $23.50  
  Purchase #5 $116.31   7.355%   $124.8646   $124.86   $124.85   $124.90  
  Purchase #6 $188.95   9.524%   $206.9456   $206.95   $206.95   $206.90  
  Purchase #7 $109.37   13.402%   $124.0278   $124.03   $124.05   $124.00  
  7 purchase totals = $548.70       $600.6775   $600.68   $600.65   $600.70