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 $23.30   11.574%   $25.9967   $26.00   $26.00   $26.00  
  Purchase #2 $110.91   7.522%   $119.2527   $119.25   $119.25   $119.30  
  Purchase #3 $106.46   12.568%   $119.8399   $119.84   $119.85   $119.80  
  Purchase #4 $140.44   12.267%   $157.6678   $157.67   $157.65   $157.70  
  Purchase #5 $185.70   13.806%   $211.3377   $211.34   $211.35   $211.30  
  Purchase #6 $205.35   10.318%   $226.538   $226.54   $226.55   $226.50  
  Purchase #7 $62.88   10.712%   $69.6157   $69.62   $69.60   $69.60  
  7 purchase totals = $835.04       $930.2485   $930.26   $930.25   $930.20