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 $59.79   9.764%   $65.6279   $65.63   $65.65   $65.60  
  Purchase #2 $230.32   13.383%   $261.1437   $261.14   $261.15   $261.10  
  Purchase #3 $191.46   7.542%   $205.8999   $205.90   $205.90   $205.90  
  Purchase #4 $40.51   10.423%   $44.7324   $44.73   $44.75   $44.70  
  Purchase #5 $131.59   7.142%   $140.9882   $140.99   $141.00   $141.00  
  Purchase #6 $11.52   3.859%   $11.9646   $11.96   $11.95   $12.00  
  Purchase #7 $151.91   13.459%   $172.3556   $172.36   $172.35   $172.40  
  7 purchase totals = $817.10       $902.7123   $902.71   $902.75   $902.70