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 $59.96   5.515%   $63.2668   $63.27   $63.25   $63.30  
  Purchase #2 $42.30   9.655%   $46.3841   $46.38   $46.40   $46.40  
  Purchase #3 $208.48   8.418%   $226.0298   $226.03   $226.05   $226.00  
  Purchase #4 $154.45   8.117%   $166.9867   $166.99   $167.00   $167.00  
  Purchase #5 $62.59   10.424%   $69.1144   $69.11   $69.10   $69.10  
  Purchase #6 $90.95   6.556%   $96.9127   $96.91   $96.90   $96.90  
  Purchase #7 $81.89   4.603%   $85.6594   $85.66   $85.65   $85.70  
  7 purchase totals = $700.62       $754.3539   $754.35   $754.35   $754.40