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 $23.46   11.300%   $26.111   $26.11   $26.10   $26.10  
  Purchase #2 $46.89   8.564%   $50.9057   $50.91   $50.90   $50.90  
  Purchase #3 $92.99   8.687%   $101.068   $101.07   $101.05   $101.10  
  Purchase #4 $44.89   7.630%   $48.3151   $48.32   $48.30   $48.30  
  Purchase #5 $236.84   11.406%   $263.854   $263.85   $263.85   $263.90  
  Purchase #6 $70.81   13.209%   $80.1633   $80.16   $80.15   $80.20  
  Purchase #7 $232.94   7.416%   $250.2148   $250.21   $250.20   $250.20  
  7 purchase totals = $748.82       $820.6319   $820.63   $820.55   $820.70