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 $119.81   5.605%   $126.5254   $126.53   $126.55   $126.50  
  Purchase #2 $50.28   13.179%   $56.9064   $56.91   $56.90   $56.90  
  Purchase #3 $154.99   10.242%   $170.8641   $170.86   $170.85   $170.90  
  Purchase #4 $91.93   9.520%   $100.6817   $100.68   $100.70   $100.70  
  Purchase #5 $146.68   3.714%   $152.1277   $152.13   $152.15   $152.10  
  Purchase #6 $120.35   8.226%   $130.25   $130.25   $130.25   $130.30  
  Purchase #7 $41.35   13.552%   $46.9538   $46.95   $46.95   $47.00  
  7 purchase totals = $725.39       $784.3091   $784.31   $784.35   $784.40