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 $42.79   12.177%   $48.0005   $48.00   $48.00   $48.00  
  Purchase #2 $168.60   3.299%   $174.1621   $174.16   $174.15   $174.20  
  Purchase #3 $93.76   8.357%   $101.5955   $101.60   $101.60   $101.60  
  Purchase #4 $26.39   10.869%   $29.2583   $29.26   $29.25   $29.30  
  Purchase #5 $230.25   6.791%   $245.8863   $245.89   $245.90   $245.90  
  Purchase #6 $201.34   7.278%   $215.9935   $215.99   $216.00   $216.00  
  Purchase #7 $37.43   8.713%   $40.6913   $40.69   $40.70   $40.70  
  7 purchase totals = $800.56       $855.5875   $855.59   $855.60   $855.70