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 $202.95   10.418%   $224.0933   $224.09   $224.10   $224.10  
  Purchase #2 $216.28   11.506%   $241.1652   $241.17   $241.15   $241.20  
  Purchase #3 $124.32   12.232%   $139.5268   $139.53   $139.55   $139.50  
  Purchase #4 $101.57   12.446%   $114.2114   $114.21   $114.20   $114.20  
  Purchase #5 $204.54   11.841%   $228.7596   $228.76   $228.75   $228.80  
  Purchase #6 $156.66   13.104%   $177.1887   $177.19   $177.20   $177.20  
  Purchase #7 $69.78   9.762%   $76.5919   $76.59   $76.60   $76.60  
  7 purchase totals = $1,076.10       $1,201.5369   $1,201.54   $1,201.55   $1,201.60