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 $249.69   5.333%   $263.006   $263.01   $263.00   $263.00  
  Purchase #2 $133.64   7.664%   $143.8822   $143.88   $143.90   $143.90  
  Purchase #3 $146.93   10.441%   $162.271   $162.27   $162.25   $162.30  
  Purchase #4 $84.77   4.724%   $88.7745   $88.77   $88.75   $88.80  
  Purchase #5 $67.48   8.619%   $73.2961   $73.30   $73.30   $73.30  
  Purchase #6 $142.26   7.495%   $152.9224   $152.92   $152.90   $152.90  
  Purchase #7 $41.40   3.612%   $42.8954   $42.90   $42.90   $42.90  
  7 purchase totals = $866.17       $927.0476   $927.05   $927.00   $927.10