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 $57.54   13.313%   $65.2003   $65.20   $65.20   $65.20  
  Purchase #2 $191.28   4.589%   $200.0578   $200.06   $200.05   $200.10  
  Purchase #3 $98.77   11.607%   $110.2342   $110.23   $110.25   $110.20  
  Purchase #4 $24.48   6.763%   $26.1356   $26.14   $26.15   $26.10  
  Purchase #5 $117.78   9.785%   $129.3048   $129.30   $129.30   $129.30  
  Purchase #6 $175.67   13.273%   $198.9867   $198.99   $199.00   $199.00  
  Purchase #7 $99.48   13.217%   $112.6283   $112.63   $112.65   $112.60  
  7 purchase totals = $765.00       $842.5477   $842.55   $842.60   $842.50