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 $24.78   5.362%   $26.1087   $26.11   $26.10   $26.10  
  Purchase #2 $227.66   8.453%   $246.9041   $246.90   $246.90   $246.90  
  Purchase #3 $231.58   10.215%   $255.2359   $255.24   $255.25   $255.20  
  Purchase #4 $20.90   8.622%   $22.702   $22.70   $22.70   $22.70  
  Purchase #5 $20.87   6.818%   $22.2929   $22.29   $22.30   $22.30  
  Purchase #6 $118.85   4.638%   $124.3623   $124.36   $124.35   $124.40  
  Purchase #7 $237.73   13.626%   $270.1231   $270.12   $270.10   $270.10  
  7 purchase totals = $882.37       $967.7290   $967.72   $967.70   $967.70