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 $80.86   5.660%   $85.4367   $85.44   $85.45   $85.40  
  Purchase #2 $174.92   12.384%   $196.5821   $196.58   $196.60   $196.60  
  Purchase #3 $192.56   11.505%   $214.714   $214.71   $214.70   $214.70  
  Purchase #4 $48.43   8.670%   $52.6289   $52.63   $52.65   $52.60  
  Purchase #5 $234.91   11.576%   $262.1032   $262.10   $262.10   $262.10  
  Purchase #6 $25.45   9.827%   $27.951   $27.95   $27.95   $28.00  
  Purchase #7 $26.78   12.415%   $30.1047   $30.10   $30.10   $30.10  
  7 purchase totals = $783.91       $869.5206   $869.51   $869.55   $869.50