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 $67.57   12.631%   $76.1048   $76.10   $76.10   $76.10  
  Purchase #2 $108.80   5.109%   $114.3586   $114.36   $114.35   $114.40  
  Purchase #3 $59.40   6.351%   $63.1725   $63.17   $63.15   $63.20  
  Purchase #4 $120.77   11.863%   $135.0969   $135.10   $135.10   $135.10  
  Purchase #5 $72.60   5.502%   $76.5945   $76.59   $76.60   $76.60  
  Purchase #6 $222.76   6.362%   $236.932   $236.93   $236.95   $236.90  
  Purchase #7 $115.31   6.227%   $122.4904   $122.49   $122.50   $122.50  
  7 purchase totals = $767.21       $824.7497   $824.74   $824.75   $824.80