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 $25.37   5.433%   $26.7484   $26.75   $26.75   $26.70  
  Purchase #2 $217.72   10.750%   $241.1249   $241.12   $241.10   $241.10  
  Purchase #3 $165.35   8.664%   $179.6759   $179.68   $179.70   $179.70  
  Purchase #4 $210.34   3.141%   $216.9468   $216.95   $216.95   $216.90  
  Purchase #5 $11.61   13.238%   $13.1469   $13.15   $13.15   $13.10  
  Purchase #6 $213.95   4.657%   $223.9137   $223.91   $223.90   $223.90  
  Purchase #7 $51.31   9.366%   $56.1157   $56.12   $56.10   $56.10  
  7 purchase totals = $895.65       $957.6723   $957.68   $957.65   $957.50