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 $64.55   6.179%   $68.5385   $68.54   $68.55   $68.50  
  Purchase #2 $110.46   3.239%   $114.0378   $114.04   $114.05   $114.00  
  Purchase #3 $43.44   8.316%   $47.0525   $47.05   $47.05   $47.10  
  Purchase #4 $130.69   6.734%   $139.4907   $139.49   $139.50   $139.50  
  Purchase #5 $205.33   3.837%   $213.2085   $213.21   $213.20   $213.20  
  Purchase #6 $32.85   3.421%   $33.9738   $33.97   $33.95   $34.00  
  Purchase #7 $135.94   6.760%   $145.1295   $145.13   $145.15   $145.10  
  7 purchase totals = $723.26       $761.4313   $761.43   $761.45   $761.40