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 $58.46   4.560%   $61.1258   $61.13   $61.15   $61.10  
  Purchase #2 $232.60   8.399%   $252.1361   $252.14   $252.15   $252.10  
  Purchase #3 $238.90   8.838%   $260.014   $260.01   $260.00   $260.00  
  Purchase #4 $77.63   9.402%   $84.9288   $84.93   $84.95   $84.90  
  Purchase #5 $140.49   13.613%   $159.6149   $159.61   $159.60   $159.60  
  Purchase #6 $70.53   5.301%   $74.2688   $74.27   $74.25   $74.30  
  Purchase #7 $250.43   9.162%   $273.3744   $273.37   $273.35   $273.40  
  7 purchase totals = $1,069.04       $1,165.4628   $1,165.46   $1,165.45   $1,165.40