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 $44.76   9.134%   $48.8484   $48.85   $48.85   $48.80  
  Purchase #2 $56.91   4.159%   $59.2769   $59.28   $59.30   $59.30  
  Purchase #3 $78.95   4.414%   $82.4349   $82.43   $82.45   $82.40  
  Purchase #4 $74.93   9.320%   $81.9135   $81.91   $81.90   $81.90  
  Purchase #5 $107.66   11.713%   $120.2702   $120.27   $120.25   $120.30  
  Purchase #6 $138.28   4.334%   $144.2731   $144.27   $144.25   $144.30  
  Purchase #7 $73.25   3.735%   $75.9859   $75.99   $76.00   $76.00  
  7 purchase totals = $574.74       $613.0029   $613.00   $613.00   $613.00