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 $208.96   13.685%   $237.5562   $237.56   $237.55   $237.60  
  Purchase #2 $34.94   6.538%   $37.2244   $37.22   $37.20   $37.20  
  Purchase #3 $140.63   12.659%   $158.4324   $158.43   $158.45   $158.40  
  Purchase #4 $84.79   12.570%   $95.4481   $95.45   $95.45   $95.40  
  Purchase #5 $224.73   10.667%   $248.7019   $248.70   $248.70   $248.70  
  Purchase #6 $215.51   6.787%   $230.1367   $230.14   $230.15   $230.10  
  Purchase #7 $11.70   13.212%   $13.2458   $13.25   $13.25   $13.20  
  7 purchase totals = $921.26       $1,020.7455   $1,020.75   $1,020.75   $1,020.60