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 $24.74   6.239%   $26.2835   $26.28   $26.30   $26.30  
  Purchase #2 $141.33   13.137%   $159.8965   $159.90   $159.90   $159.90  
  Purchase #3 $68.34   8.756%   $74.3239   $74.32   $74.30   $74.30  
  Purchase #4 $167.37   6.746%   $178.6608   $178.66   $178.65   $178.70  
  Purchase #5 $41.45   3.750%   $43.0044   $43.00   $43.00   $43.00  
  Purchase #6 $129.64   3.619%   $134.3317   $134.33   $134.35   $134.30  
  Purchase #7 $210.51   10.451%   $232.5104   $232.51   $232.50   $232.50  
  7 purchase totals = $783.38       $849.0112   $849.00   $849.00   $849.00