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 $22.94   4.599%   $23.995   $24.00   $24.00   $24.00  
  Purchase #2 $208.42   13.208%   $235.9481   $235.95   $235.95   $235.90  
  Purchase #3 $14.43   8.268%   $15.6231   $15.62   $15.60   $15.60  
  Purchase #4 $97.87   11.378%   $109.0056   $109.01   $109.00   $109.00  
  Purchase #5 $54.33   5.588%   $57.366   $57.37   $57.35   $57.40  
  Purchase #6 $63.80   5.193%   $67.1131   $67.11   $67.10   $67.10  
  Purchase #7 $188.38   5.794%   $199.2947   $199.29   $199.30   $199.30  
  7 purchase totals = $650.17       $708.3456   $708.35   $708.30   $708.30