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 $86.28   10.629%   $95.4507   $95.45   $95.45   $95.50  
  Purchase #2 $201.57   3.162%   $207.9436   $207.94   $207.95   $207.90  
  Purchase #3 $7.71   11.610%   $8.6051   $8.61   $8.60   $8.60  
  Purchase #4 $123.82   3.856%   $128.5945   $128.59   $128.60   $128.60  
  Purchase #5 $157.99   13.188%   $178.8257   $178.83   $178.85   $178.80  
  Purchase #6 $180.99   4.648%   $189.4024   $189.40   $189.40   $189.40  
  Purchase #7 $157.26   3.495%   $162.7562   $162.76   $162.75   $162.80  
  7 purchase totals = $915.62       $971.5782   $971.58   $971.60   $971.60