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 $136.25   11.287%   $151.6285   $151.63   $151.65   $151.60  
  Purchase #2 $79.27   6.466%   $84.3956   $84.40   $84.40   $84.40  
  Purchase #3 $193.66   10.263%   $213.5353   $213.54   $213.55   $213.50  
  Purchase #4 $95.58   11.808%   $106.8661   $106.87   $106.85   $106.90  
  Purchase #5 $62.63   11.173%   $69.6276   $69.63   $69.65   $69.60  
  Purchase #6 $27.31   12.184%   $30.6375   $30.64   $30.65   $30.60  
  Purchase #7 $103.30   3.194%   $106.5994   $106.60   $106.60   $106.60  
  7 purchase totals = $698.00       $763.2900   $763.31   $763.35   $763.20