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 $105.97   13.144%   $119.8987   $119.90   $119.90   $119.90  
  Purchase #2 $196.96   4.561%   $205.9433   $205.94   $205.95   $205.90  
  Purchase #3 $122.58   7.758%   $132.0898   $132.09   $132.10   $132.10  
  Purchase #4 $82.87   3.195%   $85.5177   $85.52   $85.50   $85.50  
  Purchase #5 $158.26   8.525%   $171.7517   $171.75   $171.75   $171.80  
  Purchase #6 $135.87   11.236%   $151.1364   $151.14   $151.15   $151.10  
  Purchase #7 $239.56   10.118%   $263.7987   $263.80   $263.80   $263.80  
  7 purchase totals = $1,042.07       $1,130.1363   $1,130.14   $1,130.15   $1,130.10