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 $59.95   4.158%   $62.4427   $62.44   $62.45   $62.40  
  Purchase #2 $22.31   11.577%   $24.8928   $24.89   $24.90   $24.90  
  Purchase #3 $217.70   11.647%   $243.0555   $243.06   $243.05   $243.10  
  Purchase #4 $168.70   9.814%   $185.2562   $185.26   $185.25   $185.30  
  Purchase #5 $107.90   13.442%   $122.4039   $122.40   $122.40   $122.40  
  Purchase #6 $11.28   4.305%   $11.7656   $11.77   $11.75   $11.80  
  Purchase #7 $127.30   10.705%   $140.9275   $140.93   $140.95   $140.90  
  7 purchase totals = $715.14       $790.7442   $790.75   $790.75   $790.80