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 $192.63   7.298%   $206.6881   $206.69   $206.70   $206.70  
  Purchase #2 $211.59   9.712%   $232.1396   $232.14   $232.15   $232.10  
  Purchase #3 $53.32   12.578%   $60.0266   $60.03   $60.05   $60.00  
  Purchase #4 $12.31   8.682%   $13.3788   $13.38   $13.40   $13.40  
  Purchase #5 $55.92   5.789%   $59.1572   $59.16   $59.15   $59.20  
  Purchase #6 $223.49   11.834%   $249.9378   $249.94   $249.95   $249.90  
  Purchase #7 $187.55   10.642%   $207.5091   $207.51   $207.50   $207.50  
  7 purchase totals = $936.81       $1,028.8372   $1,028.85   $1,028.90   $1,028.80