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 $24.92   6.208%   $26.467   $26.47   $26.45   $26.50  
  Purchase #2 $26.60   4.308%   $27.7459   $27.75   $27.75   $27.70  
  Purchase #3 $5.84   3.547%   $6.0471   $6.05   $6.05   $6.00  
  Purchase #4 $67.63   7.310%   $72.5738   $72.57   $72.55   $72.60  
  Purchase #5 $56.40   4.259%   $58.8021   $58.80   $58.80   $58.80  
  Purchase #6 $230.65   13.212%   $261.1235   $261.12   $261.10   $261.10  
  Purchase #7 $218.69   13.278%   $247.7277   $247.73   $247.75   $247.70  
  7 purchase totals = $630.73       $700.4871   $700.49   $700.45   $700.40