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 $34.84   11.237%   $38.755   $38.76   $38.75   $38.80  
  Purchase #2 $173.57   8.648%   $188.5803   $188.58   $188.60   $188.60  
  Purchase #3 $114.58   6.190%   $121.6725   $121.67   $121.65   $121.70  
  Purchase #4 $119.83   5.809%   $126.7909   $126.79   $126.80   $126.80  
  Purchase #5 $230.34   5.169%   $242.2463   $242.25   $242.25   $242.20  
  Purchase #6 $218.93   8.654%   $237.8762   $237.88   $237.90   $237.90  
  Purchase #7 $61.27   3.551%   $63.4457   $63.45   $63.45   $63.40  
  7 purchase totals = $953.36       $1,019.3669   $1,019.38   $1,019.40   $1,019.40