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 $63.81   3.822%   $66.2488   $66.25   $66.25   $66.20  
  Purchase #2 $108.40   5.471%   $114.3306   $114.33   $114.35   $114.30  
  Purchase #3 $177.33   4.827%   $185.8897   $185.89   $185.90   $185.90  
  Purchase #4 $108.75   12.258%   $122.0806   $122.08   $122.10   $122.10  
  Purchase #5 $136.84   3.263%   $141.3051   $141.31   $141.30   $141.30  
  Purchase #6 $62.46   13.208%   $70.7097   $70.71   $70.70   $70.70  
  Purchase #7 $122.27   6.159%   $129.8006   $129.80   $129.80   $129.80  
  7 purchase totals = $779.86       $830.3651   $830.37   $830.40   $830.30