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 $56.82   11.580%   $63.3998   $63.40   $63.40   $63.40  
  Purchase #2 $214.92   3.810%   $223.1085   $223.11   $223.10   $223.10  
  Purchase #3 $158.88   8.742%   $172.7693   $172.77   $172.75   $172.80  
  Purchase #4 $170.67   7.177%   $182.919   $182.92   $182.90   $182.90  
  Purchase #5 $60.82   4.615%   $63.6268   $63.63   $63.65   $63.60  
  Purchase #6 $144.46   10.732%   $159.9634   $159.96   $159.95   $160.00  
  Purchase #7 $163.25   8.552%   $177.2111   $177.21   $177.20   $177.20  
  7 purchase totals = $969.82       $1,042.9979   $1,043.00   $1,042.95   $1,043.00