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 $138.91   4.688%   $145.4221   $145.42   $145.40   $145.40  
  Purchase #2 $51.95   3.546%   $53.7921   $53.79   $53.80   $53.80  
  Purchase #3 $160.63   5.339%   $169.206   $169.21   $169.20   $169.20  
  Purchase #4 $166.41   11.766%   $185.9898   $185.99   $186.00   $186.00  
  Purchase #5 $51.92   13.353%   $58.8529   $58.85   $58.85   $58.90  
  Purchase #6 $65.81   7.325%   $70.6306   $70.63   $70.65   $70.60  
  Purchase #7 $31.32   8.217%   $33.8936   $33.89   $33.90   $33.90  
  7 purchase totals = $666.95       $717.7871   $717.78   $717.80   $717.80