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 $23.66   13.492%   $26.8522   $26.85   $26.85   $26.90  
  Purchase #2 $73.90   13.246%   $83.6888   $83.69   $83.70   $83.70  
  Purchase #3 $131.97   8.459%   $143.1333   $143.13   $143.15   $143.10  
  Purchase #4 $234.79   9.247%   $256.501   $256.50   $256.50   $256.50  
  Purchase #5 $103.55   9.602%   $113.4929   $113.49   $113.50   $113.50  
  Purchase #6 $5.52   10.109%   $6.078   $6.08   $6.10   $6.10  
  Purchase #7 $136.66   3.628%   $141.618   $141.62   $141.60   $141.60  
  7 purchase totals = $710.05       $771.3642   $771.36   $771.40   $771.40