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 $24.61   4.867%   $25.8078   $25.81   $25.80   $25.80  
  Purchase #2 $54.51   10.147%   $60.0411   $60.04   $60.05   $60.00  
  Purchase #3 $110.97   12.359%   $124.6848   $124.68   $124.70   $124.70  
  Purchase #4 $199.72   13.423%   $226.5284   $226.53   $226.55   $226.50  
  Purchase #5 $165.70   13.800%   $188.5666   $188.57   $188.55   $188.60  
  Purchase #6 $120.75   12.649%   $136.0237   $136.02   $136.00   $136.00  
  Purchase #7 $22.36   7.542%   $24.0464   $24.05   $24.05   $24.00  
  7 purchase totals = $698.62       $785.6988   $785.70   $785.70   $785.60