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 $186.61   6.647%   $199.014   $199.01   $199.00   $199.00  
  Purchase #2 $78.90   5.792%   $83.4699   $83.47   $83.45   $83.50  
  Purchase #3 $19.86   11.424%   $22.1288   $22.13   $22.15   $22.10  
  Purchase #4 $200.33   8.869%   $218.0973   $218.10   $218.10   $218.10  
  Purchase #5 $115.55   5.673%   $122.1052   $122.11   $122.10   $122.10  
  Purchase #6 $11.76   5.458%   $12.4019   $12.40   $12.40   $12.40  
  Purchase #7 $197.30   5.838%   $208.8184   $208.82   $208.80   $208.80  
  7 purchase totals = $810.31       $866.0355   $866.04   $866.00   $866.00