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 $54.55   13.675%   $62.0097   $62.01   $62.00   $62.00  
  Purchase #2 $44.76   6.731%   $47.7728   $47.77   $47.75   $47.80  
  Purchase #3 $237.54   7.520%   $255.403   $255.40   $255.40   $255.40  
  Purchase #4 $63.73   9.678%   $69.8978   $69.90   $69.90   $69.90  
  Purchase #5 $137.70   3.311%   $142.2592   $142.26   $142.25   $142.30  
  Purchase #6 $74.64   12.688%   $84.1103   $84.11   $84.10   $84.10  
  Purchase #7 $168.95   10.147%   $186.0934   $186.09   $186.10   $186.10  
  7 purchase totals = $781.87       $847.5462   $847.54   $847.50   $847.60