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 $55.56   5.467%   $58.5975   $58.60   $58.60   $58.60  
  Purchase #2 $119.66   11.767%   $133.7404   $133.74   $133.75   $133.70  
  Purchase #3 $159.57   9.520%   $174.7611   $174.76   $174.75   $174.80  
  Purchase #4 $6.39   13.840%   $7.2744   $7.27   $7.25   $7.30  
  Purchase #5 $249.72   7.835%   $269.2856   $269.29   $269.30   $269.30  
  Purchase #6 $174.70   5.326%   $184.0045   $184.00   $184.00   $184.00  
  Purchase #7 $220.81   3.242%   $227.9687   $227.97   $227.95   $228.00  
  7 purchase totals = $986.41       $1,055.6322   $1,055.63   $1,055.60   $1,055.70