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 $52.78   11.866%   $59.0429   $59.04   $59.05   $59.00  
  Purchase #2 $100.90   13.563%   $114.5851   $114.59   $114.60   $114.60  
  Purchase #3 $25.37   6.509%   $27.0213   $27.02   $27.00   $27.00  
  Purchase #4 $198.33   8.465%   $215.1186   $215.12   $215.10   $215.10  
  Purchase #5 $153.49   8.313%   $166.2496   $166.25   $166.25   $166.20  
  Purchase #6 $124.95   10.803%   $138.4483   $138.45   $138.45   $138.40  
  Purchase #7 $206.94   9.489%   $226.5765   $226.58   $226.60   $226.60  
  7 purchase totals = $862.76       $947.0423   $947.05   $947.05   $946.90