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 $201.58   5.303%   $212.2698   $212.27   $212.25   $212.30  
  Purchase #2 $248.41   3.398%   $256.851   $256.85   $256.85   $256.90  
  Purchase #3 $78.91   9.311%   $86.2573   $86.26   $86.25   $86.30  
  Purchase #4 $6.90   10.597%   $7.6312   $7.63   $7.65   $7.60  
  Purchase #5 $230.58   4.432%   $240.7993   $240.80   $240.80   $240.80  
  Purchase #6 $119.94   12.560%   $135.0045   $135.00   $135.00   $135.00  
  Purchase #7 $216.40   8.477%   $234.7442   $234.74   $234.75   $234.70  
  7 purchase totals = $1,102.72       $1,173.5573   $1,173.55   $1,173.55   $1,173.60