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 $60.54   4.357%   $63.1777   $63.18   $63.20   $63.20  
  Purchase #2 $213.66   13.186%   $241.8332   $241.83   $241.85   $241.80  
  Purchase #3 $173.42   6.149%   $184.0836   $184.08   $184.10   $184.10  
  Purchase #4 $228.61   5.648%   $241.5219   $241.52   $241.50   $241.50  
  Purchase #5 $98.51   7.334%   $105.7347   $105.73   $105.75   $105.70  
  Purchase #6 $25.51   4.273%   $26.6   $26.60   $26.60   $26.60  
  Purchase #7 $86.75   10.209%   $95.6063   $95.61   $95.60   $95.60  
  7 purchase totals = $887.00       $958.5574   $958.55   $958.60   $958.50