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 $108.27   3.459%   $112.0151   $112.02   $112.00   $112.00  
  Purchase #2 $201.86   11.192%   $224.4522   $224.45   $224.45   $224.50  
  Purchase #3 $237.52   5.519%   $250.6287   $250.63   $250.65   $250.60  
  Purchase #4 $111.41   6.552%   $118.7096   $118.71   $118.70   $118.70  
  Purchase #5 $158.73   5.297%   $167.1379   $167.14   $167.15   $167.10  
  Purchase #6 $23.87   12.598%   $26.8771   $26.88   $26.90   $26.90  
  Purchase #7 $58.48   8.460%   $63.4274   $63.43   $63.45   $63.40  
  7 purchase totals = $900.14       $963.2480   $963.26   $963.30   $963.20