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 $24.74   7.632%   $26.6282   $26.63   $26.65   $26.60  
  Purchase #2 $143.39   12.763%   $161.6909   $161.69   $161.70   $161.70  
  Purchase #3 $166.85   12.496%   $187.6996   $187.70   $187.70   $187.70  
  Purchase #4 $51.62   6.337%   $54.8912   $54.89   $54.90   $54.90  
  Purchase #5 $165.67   4.675%   $173.4151   $173.42   $173.40   $173.40  
  Purchase #6 $104.90   10.518%   $115.9334   $115.93   $115.95   $115.90  
  Purchase #7 $113.36   6.359%   $120.5686   $120.57   $120.55   $120.60  
  7 purchase totals = $770.53       $840.8270   $840.83   $840.85   $840.80