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 $57.59   10.200%   $63.4642   $63.46   $63.45   $63.50  
  Purchase #2 $125.71   5.363%   $132.4518   $132.45   $132.45   $132.50  
  Purchase #3 $114.83   11.746%   $128.3179   $128.32   $128.30   $128.30  
  Purchase #4 $231.54   8.677%   $251.6307   $251.63   $251.65   $251.60  
  Purchase #5 $248.65   5.385%   $262.0398   $262.04   $262.05   $262.00  
  Purchase #6 $99.78   4.497%   $104.2671   $104.27   $104.25   $104.30  
  Purchase #7 $56.89   13.291%   $64.4512   $64.45   $64.45   $64.50  
  7 purchase totals = $934.99       $1,006.6227   $1,006.62   $1,006.60   $1,006.70