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 $25.66   3.788%   $26.632   $26.63   $26.65   $26.60  
  Purchase #2 $130.65   9.522%   $143.0905   $143.09   $143.10   $143.10  
  Purchase #3 $60.39   6.153%   $64.1058   $64.11   $64.10   $64.10  
  Purchase #4 $232.31   6.394%   $247.1639   $247.16   $247.15   $247.20  
  Purchase #5 $179.86   5.383%   $189.5419   $189.54   $189.55   $189.50  
  Purchase #6 $220.37   10.646%   $243.8306   $243.83   $243.85   $243.80  
  Purchase #7 $101.72   13.247%   $115.1948   $115.19   $115.20   $115.20  
  7 purchase totals = $950.96       $1,029.5595   $1,029.55   $1,029.60   $1,029.50