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 $208.52   11.597%   $232.7021   $232.70   $232.70   $232.70  
  Purchase #2 $199.94   6.330%   $212.5962   $212.60   $212.60   $212.60  
  Purchase #3 $100.95   11.335%   $112.3927   $112.39   $112.40   $112.40  
  Purchase #4 $162.89   5.271%   $171.4759   $171.48   $171.50   $171.50  
  Purchase #5 $70.82   7.106%   $75.8525   $75.85   $75.85   $75.90  
  Purchase #6 $76.49   12.186%   $85.8111   $85.81   $85.80   $85.80  
  Purchase #7 $129.74   6.137%   $137.7021   $137.70   $137.70   $137.70  
  7 purchase totals = $949.35       $1,028.5326   $1,028.53   $1,028.55   $1,028.60