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 $41.33   10.462%   $45.6539   $45.65   $45.65   $45.70  
  Purchase #2 $85.61   6.822%   $91.4503   $91.45   $91.45   $91.50  
  Purchase #3 $52.26   7.583%   $56.2229   $56.22   $56.20   $56.20  
  Purchase #4 $59.69   8.819%   $64.9541   $64.95   $64.95   $65.00  
  Purchase #5 $125.73   9.384%   $137.5285   $137.53   $137.55   $137.50  
  Purchase #6 $193.69   6.671%   $206.6111   $206.61   $206.60   $206.60  
  Purchase #7 $224.62   10.427%   $248.0411   $248.04   $248.05   $248.00  
  7 purchase totals = $782.93       $850.4619   $850.45   $850.45   $850.50