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 $181.84   11.846%   $203.3808   $203.38   $203.40   $203.40  
  Purchase #2 $247.69   9.491%   $271.1983   $271.20   $271.20   $271.20  
  Purchase #3 $69.71   8.490%   $75.6284   $75.63   $75.65   $75.60  
  Purchase #4 $232.53   6.872%   $248.5095   $248.51   $248.50   $248.50  
  Purchase #5 $196.27   12.593%   $220.9863   $220.99   $221.00   $221.00  
  Purchase #6 $206.44   4.174%   $215.0568   $215.06   $215.05   $215.10  
  Purchase #7 $200.84   13.642%   $228.2386   $228.24   $228.25   $228.20  
  7 purchase totals = $1,335.32       $1,462.9987   $1,463.01   $1,463.05   $1,463.00