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 $23.79   9.422%   $26.0315   $26.03   $26.05   $26.00  
  Purchase #2 $198.94   6.199%   $211.2723   $211.27   $211.25   $211.30  
  Purchase #3 $37.46   11.246%   $41.6728   $41.67   $41.65   $41.70  
  Purchase #4 $151.40   5.647%   $159.9496   $159.95   $159.95   $159.90  
  Purchase #5 $168.51   8.844%   $183.413   $183.41   $183.40   $183.40  
  Purchase #6 $86.60   13.360%   $98.1698   $98.17   $98.15   $98.20  
  Purchase #7 $87.85   9.327%   $96.0438   $96.04   $96.05   $96.00  
  7 purchase totals = $754.55       $816.5528   $816.54   $816.50   $816.50