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 $14.59   4.523%   $15.2499   $15.25   $15.25   $15.20  
  Purchase #2 $211.54   8.490%   $229.4997   $229.50   $229.50   $229.50  
  Purchase #3 $160.32   4.828%   $168.0602   $168.06   $168.05   $168.10  
  Purchase #4 $100.48   7.329%   $107.8442   $107.84   $107.85   $107.80  
  Purchase #5 $199.94   6.769%   $213.4739   $213.47   $213.45   $213.50  
  Purchase #6 $208.64   12.847%   $235.444   $235.44   $235.45   $235.40  
  Purchase #7 $191.60   8.535%   $207.9531   $207.95   $207.95   $208.00  
  7 purchase totals = $1,087.11       $1,177.5250   $1,177.51   $1,177.50   $1,177.50