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 $165.77   7.344%   $177.9441   $177.94   $177.95   $177.90  
  Purchase #2 $172.71   8.590%   $187.5458   $187.55   $187.55   $187.50  
  Purchase #3 $15.68   5.757%   $16.5827   $16.58   $16.60   $16.60  
  Purchase #4 $53.80   13.783%   $61.2153   $61.22   $61.20   $61.20  
  Purchase #5 $249.70   5.252%   $262.8142   $262.81   $262.80   $262.80  
  Purchase #6 $185.98   6.624%   $198.2993   $198.30   $198.30   $198.30  
  Purchase #7 $10.69   11.197%   $11.887   $11.89   $11.90   $11.90  
  7 purchase totals = $854.33       $916.2884   $916.29   $916.30   $916.20