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 $60.81   11.793%   $67.9813   $67.98   $68.00   $68.00  
  Purchase #2 $62.58   10.242%   $68.9894   $68.99   $69.00   $69.00  
  Purchase #3 $41.78   11.736%   $46.6833   $46.68   $46.70   $46.70  
  Purchase #4 $197.71   3.724%   $205.0727   $205.07   $205.05   $205.10  
  Purchase #5 $199.84   13.225%   $226.2688   $226.27   $226.25   $226.30  
  Purchase #6 $12.91   5.768%   $13.6546   $13.65   $13.65   $13.70  
  Purchase #7 $138.67   7.445%   $148.994   $148.99   $149.00   $149.00  
  7 purchase totals = $714.30       $777.6441   $777.63   $777.65   $777.80