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 $56.71   11.212%   $63.0683   $63.07   $63.05   $63.10  
  Purchase #2 $102.57   6.799%   $109.5437   $109.54   $109.55   $109.50  
  Purchase #3 $11.37   3.754%   $11.7968   $11.80   $11.80   $11.80  
  Purchase #4 $141.28   12.737%   $159.2748   $159.27   $159.25   $159.30  
  Purchase #5 $236.84   5.852%   $250.6999   $250.70   $250.70   $250.70  
  Purchase #6 $239.91   3.596%   $248.5372   $248.54   $248.55   $248.50  
  Purchase #7 $106.64   4.853%   $111.8152   $111.82   $111.80   $111.80  
  7 purchase totals = $895.32       $954.7359   $954.74   $954.70   $954.70