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 $194.44   6.796%   $207.6541   $207.65   $207.65   $207.70  
  Purchase #2 $246.81   13.142%   $279.2458   $279.25   $279.25   $279.20  
  Purchase #3 $23.38   12.860%   $26.3867   $26.39   $26.40   $26.40  
  Purchase #4 $152.88   8.870%   $166.4405   $166.44   $166.45   $166.40  
  Purchase #5 $246.47   13.619%   $280.0367   $280.04   $280.05   $280.00  
  Purchase #6 $68.82   3.324%   $71.1076   $71.11   $71.10   $71.10  
  Purchase #7 $131.32   3.872%   $136.4047   $136.40   $136.40   $136.40  
  7 purchase totals = $1,064.12       $1,167.2761   $1,167.28   $1,167.30   $1,167.20