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 $243.49   9.837%   $267.4421   $267.44   $267.45   $267.40  
  Purchase #2 $233.83   12.349%   $262.7057   $262.71   $262.70   $262.70  
  Purchase #3 $119.93   11.551%   $133.7831   $133.78   $133.80   $133.80  
  Purchase #4 $141.86   11.212%   $157.7653   $157.77   $157.75   $157.80  
  Purchase #5 $154.72   11.581%   $172.6381   $172.64   $172.65   $172.60  
  Purchase #6 $77.94   10.448%   $86.0832   $86.08   $86.10   $86.10  
  Purchase #7 $30.41   12.816%   $34.3073   $34.31   $34.30   $34.30  
  7 purchase totals = $1,002.18       $1,114.7248   $1,114.73   $1,114.75   $1,114.70