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 $233.96   10.711%   $259.0195   $259.02   $259.00   $259.00  
  Purchase #2 $183.94   4.841%   $192.8445   $192.84   $192.85   $192.80  
  Purchase #3 $154.61   3.786%   $160.4635   $160.46   $160.45   $160.50  
  Purchase #4 $216.64   4.506%   $226.4018   $226.40   $226.40   $226.40  
  Purchase #5 $14.87   5.598%   $15.7024   $15.70   $15.70   $15.70  
  Purchase #6 $179.90   4.504%   $188.0027   $188.00   $188.00   $188.00  
  Purchase #7 $10.38   13.851%   $11.8177   $11.82   $11.80   $11.80  
  7 purchase totals = $994.30       $1,054.2521   $1,054.24   $1,054.20   $1,054.20