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 $114.51   3.343%   $118.3381   $118.34   $118.35   $118.30  
  Purchase #2 $60.54   3.390%   $62.5923   $62.59   $62.60   $62.60  
  Purchase #3 $244.46   13.455%   $277.3521   $277.35   $277.35   $277.40  
  Purchase #4 $16.34   12.837%   $18.4376   $18.44   $18.45   $18.40  
  Purchase #5 $86.82   11.337%   $96.6628   $96.66   $96.65   $96.70  
  Purchase #6 $107.62   6.264%   $114.3613   $114.36   $114.35   $114.40  
  Purchase #7 $173.25   3.587%   $179.4645   $179.46   $179.45   $179.50  
  7 purchase totals = $803.54       $867.2087   $867.20   $867.20   $867.30