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 $49.96   5.194%   $52.5549   $52.55   $52.55   $52.60  
  Purchase #2 $106.93   11.571%   $119.3029   $119.30   $119.30   $119.30  
  Purchase #3 $96.27   10.390%   $106.2725   $106.27   $106.25   $106.30  
  Purchase #4 $151.72   6.868%   $162.1401   $162.14   $162.15   $162.10  
  Purchase #5 $129.83   5.490%   $136.9577   $136.96   $136.95   $137.00  
  Purchase #6 $40.50   3.654%   $41.9799   $41.98   $42.00   $42.00  
  Purchase #7 $235.64   5.233%   $247.971   $247.97   $247.95   $248.00  
  7 purchase totals = $810.85       $867.1790   $867.17   $867.15   $867.30