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 $248.42   5.590%   $262.3067   $262.31   $262.30   $262.30  
  Purchase #2 $148.29   10.228%   $163.4571   $163.46   $163.45   $163.50  
  Purchase #3 $53.27   8.284%   $57.6829   $57.68   $57.70   $57.70  
  Purchase #4 $60.92   11.685%   $68.0385   $68.04   $68.05   $68.00  
  Purchase #5 $67.58   4.778%   $70.809   $70.81   $70.80   $70.80  
  Purchase #6 $63.83   11.785%   $71.3524   $71.35   $71.35   $71.40  
  Purchase #7 $45.33   6.853%   $48.4365   $48.44   $48.45   $48.40  
  7 purchase totals = $687.64       $742.0831   $742.09   $742.10   $742.10