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 $23.74   10.791%   $26.3018   $26.30   $26.30   $26.30  
  Purchase #2 $178.83   7.540%   $192.3138   $192.31   $192.30   $192.30  
  Purchase #3 $69.26   3.314%   $71.5553   $71.56   $71.55   $71.60  
  Purchase #4 $15.65   11.133%   $17.3923   $17.39   $17.40   $17.40  
  Purchase #5 $88.69   5.204%   $93.3054   $93.31   $93.30   $93.30  
  Purchase #6 $57.91   11.807%   $64.7474   $64.75   $64.75   $64.70  
  Purchase #7 $231.81   10.834%   $256.9243   $256.92   $256.90   $256.90  
  7 purchase totals = $665.89       $722.5403   $722.54   $722.50   $722.50