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 $246.87   5.413%   $260.2331   $260.23   $260.25   $260.20  
  Purchase #2 $105.92   13.178%   $119.8781   $119.88   $119.90   $119.90  
  Purchase #3 $60.43   9.324%   $66.0645   $66.06   $66.05   $66.10  
  Purchase #4 $187.99   5.299%   $197.9516   $197.95   $197.95   $198.00  
  Purchase #5 $126.90   5.263%   $133.5787   $133.58   $133.60   $133.60  
  Purchase #6 $64.26   13.652%   $73.0328   $73.03   $73.05   $73.00  
  Purchase #7 $109.95   4.744%   $115.166   $115.17   $115.15   $115.20  
  7 purchase totals = $902.32       $965.9048   $965.90   $965.95   $966.00