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 $186.99   10.677%   $206.9549   $206.95   $206.95   $207.00  
  Purchase #2 $129.77   8.126%   $140.3151   $140.32   $140.30   $140.30  
  Purchase #3 $74.66   9.485%   $81.7415   $81.74   $81.75   $81.70  
  Purchase #4 $222.71   8.869%   $242.4621   $242.46   $242.45   $242.50  
  Purchase #5 $162.50   12.217%   $182.3526   $182.35   $182.35   $182.40  
  Purchase #6 $57.94   4.766%   $60.7014   $60.70   $60.70   $60.70  
  Purchase #7 $156.60   13.247%   $177.3448   $177.34   $177.35   $177.30  
  7 purchase totals = $991.17       $1,091.8724   $1,091.86   $1,091.85   $1,091.90