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 $32.62   9.153%   $35.6057   $35.61   $35.60   $35.60  
  Purchase #2 $246.25   3.127%   $253.9502   $253.95   $253.95   $254.00  
  Purchase #3 $94.49   11.709%   $105.5538   $105.55   $105.55   $105.60  
  Purchase #4 $47.97   7.149%   $51.3994   $51.40   $51.40   $51.40  
  Purchase #5 $73.67   3.850%   $76.5063   $76.51   $76.50   $76.50  
  Purchase #6 $42.40   11.357%   $47.2154   $47.22   $47.20   $47.20  
  Purchase #7 $26.94   10.595%   $29.7943   $29.79   $29.80   $29.80  
  7 purchase totals = $564.34       $600.0251   $600.03   $600.00   $600.10