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 $134.97   9.368%   $147.614   $147.61   $147.60   $147.60  
  Purchase #2 $217.72   7.602%   $234.2711   $234.27   $234.25   $234.30  
  Purchase #3 $66.51   7.383%   $71.4204   $71.42   $71.40   $71.40  
  Purchase #4 $152.94   6.581%   $163.005   $163.01   $163.00   $163.00  
  Purchase #5 $76.67   9.761%   $84.1538   $84.15   $84.15   $84.20  
  Purchase #6 $97.76   3.738%   $101.4143   $101.41   $101.40   $101.40  
  Purchase #7 $44.58   12.838%   $50.3032   $50.30   $50.30   $50.30  
  7 purchase totals = $791.15       $852.1818   $852.17   $852.10   $852.20