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 $241.54   8.772%   $262.7279   $262.73   $262.75   $262.70  
  Purchase #2 $73.54   11.705%   $82.1479   $82.15   $82.15   $82.10  
  Purchase #3 $48.26   8.288%   $52.2598   $52.26   $52.25   $52.30  
  Purchase #4 $97.71   7.571%   $105.1076   $105.11   $105.10   $105.10  
  Purchase #5 $73.41   13.553%   $83.3593   $83.36   $83.35   $83.40  
  Purchase #6 $198.57   3.239%   $205.0017   $205.00   $205.00   $205.00  
  Purchase #7 $142.37   3.355%   $147.1465   $147.15   $147.15   $147.10  
  7 purchase totals = $875.40       $937.7507   $937.76   $937.75   $937.70