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 $98.25   8.590%   $106.6897   $106.69   $106.70   $106.70  
  Purchase #2 $23.67   3.556%   $24.5117   $24.51   $24.50   $24.50  
  Purchase #3 $72.32   6.713%   $77.1748   $77.17   $77.15   $77.20  
  Purchase #4 $150.81   10.404%   $166.5003   $166.50   $166.50   $166.50  
  Purchase #5 $118.56   13.830%   $134.9568   $134.96   $134.95   $135.00  
  Purchase #6 $52.90   9.414%   $57.88   $57.88   $57.90   $57.90  
  Purchase #7 $157.66   11.801%   $176.2655   $176.27   $176.25   $176.30  
  7 purchase totals = $674.17       $743.9788   $743.98   $743.95   $744.10