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 $48.86   11.240%   $54.3519   $54.35   $54.35   $54.40  
  Purchase #2 $79.87   13.346%   $90.5295   $90.53   $90.55   $90.50  
  Purchase #3 $208.49   3.614%   $216.0248   $216.02   $216.00   $216.00  
  Purchase #4 $19.48   6.552%   $20.7563   $20.76   $20.75   $20.80  
  Purchase #5 $194.72   12.248%   $218.5693   $218.57   $218.55   $218.60  
  Purchase #6 $81.74   5.217%   $86.0044   $86.00   $86.00   $86.00  
  Purchase #7 $224.74   11.563%   $250.7267   $250.73   $250.75   $250.70  
  7 purchase totals = $857.90       $936.9629   $936.96   $936.95   $937.00