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 $198.83   3.871%   $206.5267   $206.53   $206.55   $206.50  
  Purchase #2 $50.97   13.306%   $57.7521   $57.75   $57.75   $57.80  
  Purchase #3 $63.40   5.560%   $66.925   $66.93   $66.95   $66.90  
  Purchase #4 $72.74   13.378%   $82.4712   $82.47   $82.45   $82.50  
  Purchase #5 $105.46   8.651%   $114.5833   $114.58   $114.60   $114.60  
  Purchase #6 $85.27   9.405%   $93.2896   $93.29   $93.30   $93.30  
  Purchase #7 $230.28   3.232%   $237.7226   $237.72   $237.70   $237.70  
  7 purchase totals = $806.95       $859.2705   $859.27   $859.30   $859.30