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 $53.26   12.481%   $59.9074   $59.91   $59.90   $59.90  
  Purchase #2 $228.26   8.787%   $248.3172   $248.32   $248.30   $248.30  
  Purchase #3 $77.43   3.784%   $80.36   $80.36   $80.35   $80.40  
  Purchase #4 $67.46   8.866%   $73.441   $73.44   $73.45   $73.40  
  Purchase #5 $162.97   12.120%   $182.722   $182.72   $182.70   $182.70  
  Purchase #6 $235.51   9.707%   $258.371   $258.37   $258.35   $258.40  
  Purchase #7 $46.63   4.535%   $48.7447   $48.74   $48.75   $48.70  
  7 purchase totals = $871.52       $951.8633   $951.86   $951.80   $951.80