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 $60.58   7.715%   $65.2537   $65.25   $65.25   $65.30  
  Purchase #2 $199.67   13.705%   $227.0348   $227.03   $227.05   $227.00  
  Purchase #3 $60.52   4.621%   $63.3166   $63.32   $63.30   $63.30  
  Purchase #4 $5.69   3.813%   $5.907   $5.91   $5.90   $5.90  
  Purchase #5 $102.91   5.831%   $108.9107   $108.91   $108.90   $108.90  
  Purchase #6 $87.43   9.650%   $95.867   $95.87   $95.85   $95.90  
  Purchase #7 $199.63   4.520%   $208.6533   $208.65   $208.65   $208.70  
  7 purchase totals = $716.43       $774.9431   $774.94   $774.90   $775.00