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 $235.45   6.609%   $251.0109   $251.01   $251.00   $251.00  
  Purchase #2 $208.47   6.428%   $221.8705   $221.87   $221.85   $221.90  
  Purchase #3 $207.72   8.587%   $225.5569   $225.56   $225.55   $225.60  
  Purchase #4 $61.60   4.322%   $64.2624   $64.26   $64.25   $64.30  
  Purchase #5 $196.36   5.680%   $207.5132   $207.51   $207.50   $207.50  
  Purchase #6 $132.48   5.632%   $139.9413   $139.94   $139.95   $139.90  
  Purchase #7 $81.51   5.508%   $85.9996   $86.00   $86.00   $86.00  
  7 purchase totals = $1,123.59       $1,196.1548   $1,196.15   $1,196.10   $1,196.20