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 $59.55   11.412%   $66.3458   $66.35   $66.35   $66.30  
  Purchase #2 $9.54   10.413%   $10.5334   $10.53   $10.55   $10.50  
  Purchase #3 $151.45   11.515%   $168.8895   $168.89   $168.90   $168.90  
  Purchase #4 $76.57   6.638%   $81.6527   $81.65   $81.65   $81.70  
  Purchase #5 $110.99   3.144%   $114.4795   $114.48   $114.50   $114.50  
  Purchase #6 $160.62   10.640%   $177.71   $177.71   $177.70   $177.70  
  Purchase #7 $170.81   5.249%   $179.7758   $179.78   $179.80   $179.80  
  7 purchase totals = $739.53       $799.3867   $799.39   $799.45   $799.40