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 $46.92   13.547%   $53.2763   $53.28   $53.30   $53.30  
  Purchase #2 $237.59   12.241%   $266.6734   $266.67   $266.65   $266.70  
  Purchase #3 $103.74   10.334%   $114.4605   $114.46   $114.45   $114.50  
  Purchase #4 $78.57   9.842%   $86.3029   $86.30   $86.30   $86.30  
  Purchase #5 $218.66   4.653%   $228.8342   $228.83   $228.85   $228.80  
  Purchase #6 $114.57   5.831%   $121.2506   $121.25   $121.25   $121.30  
  Purchase #7 $199.45   3.277%   $205.986   $205.99   $206.00   $206.00  
  7 purchase totals = $999.50       $1,076.7839   $1,076.78   $1,076.80   $1,076.90