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 $118.68   13.432%   $134.6211   $134.62   $134.60   $134.60  
  Purchase #2 $75.39   3.118%   $77.7407   $77.74   $77.75   $77.70  
  Purchase #3 $108.95   9.832%   $119.662   $119.66   $119.65   $119.70  
  Purchase #4 $67.40   9.289%   $73.6608   $73.66   $73.65   $73.70  
  Purchase #5 $54.47   12.397%   $61.2226   $61.22   $61.20   $61.20  
  Purchase #6 $108.95   5.462%   $114.9008   $114.90   $114.90   $114.90  
  Purchase #7 $118.81   12.192%   $133.2953   $133.30   $133.30   $133.30  
  7 purchase totals = $652.65       $715.1033   $715.10   $715.05   $715.10