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 $227.62   6.752%   $242.9889   $242.99   $243.00   $243.00  
  Purchase #2 $202.89   11.415%   $226.0499   $226.05   $226.05   $226.00  
  Purchase #3 $55.53   11.500%   $61.916   $61.92   $61.90   $61.90  
  Purchase #4 $237.30   4.871%   $248.8589   $248.86   $248.85   $248.90  
  Purchase #5 $236.99   6.847%   $253.2167   $253.22   $253.20   $253.20  
  Purchase #6 $79.51   13.511%   $90.2526   $90.25   $90.25   $90.30  
  Purchase #7 $32.48   4.688%   $34.0027   $34.00   $34.00   $34.00  
  7 purchase totals = $1,072.32       $1,157.2857   $1,157.29   $1,157.25   $1,157.30