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 $54.76   6.408%   $58.269   $58.27   $58.25   $58.30  
  Purchase #2 $13.77   4.722%   $14.4202   $14.42   $14.40   $14.40  
  Purchase #3 $51.40   7.678%   $55.3465   $55.35   $55.35   $55.30  
  Purchase #4 $229.47   11.420%   $255.6755   $255.68   $255.70   $255.70  
  Purchase #5 $222.57   11.242%   $247.5913   $247.59   $247.60   $247.60  
  Purchase #6 $157.84   10.712%   $174.7478   $174.75   $174.75   $174.70  
  Purchase #7 $227.95   13.445%   $258.5979   $258.60   $258.60   $258.60  
  7 purchase totals = $957.76       $1,064.6482   $1,064.66   $1,064.65   $1,064.60