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 $229.46   5.109%   $241.1831   $241.18   $241.20   $241.20  
  Purchase #2 $177.68   3.335%   $183.6056   $183.61   $183.60   $183.60  
  Purchase #3 $10.71   7.115%   $11.472   $11.47   $11.45   $11.50  
  Purchase #4 $100.44   10.265%   $110.7502   $110.75   $110.75   $110.80  
  Purchase #5 $33.51   13.462%   $38.0211   $38.02   $38.00   $38.00  
  Purchase #6 $234.69   10.706%   $259.8159   $259.82   $259.80   $259.80  
  Purchase #7 $197.77   13.456%   $224.3819   $224.38   $224.40   $224.40  
  7 purchase totals = $984.26       $1,069.2298   $1,069.23   $1,069.20   $1,069.30