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 $23.77   11.142%   $26.4185   $26.42   $26.40   $26.40  
  Purchase #2 $96.87   5.663%   $102.3557   $102.36   $102.35   $102.40  
  Purchase #3 $225.55   7.359%   $242.1482   $242.15   $242.15   $242.10  
  Purchase #4 $90.90   3.248%   $93.8524   $93.85   $93.85   $93.90  
  Purchase #5 $79.64   11.202%   $88.5613   $88.56   $88.55   $88.60  
  Purchase #6 $11.67   6.684%   $12.45   $12.45   $12.45   $12.50  
  Purchase #7 $32.60   5.211%   $34.2988   $34.30   $34.30   $34.30  
  7 purchase totals = $561.00       $600.0849   $600.09   $600.05   $600.20