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 $57.53   6.121%   $61.0514   $61.05   $61.05   $61.10  
  Purchase #2 $187.88   6.116%   $199.3707   $199.37   $199.35   $199.40  
  Purchase #3 $89.99   7.533%   $96.7689   $96.77   $96.75   $96.80  
  Purchase #4 $13.68   9.437%   $14.971   $14.97   $14.95   $15.00  
  Purchase #5 $94.35   11.787%   $105.471   $105.47   $105.45   $105.50  
  Purchase #6 $93.56   8.284%   $101.3105   $101.31   $101.30   $101.30  
  Purchase #7 $215.65   9.757%   $236.691   $236.69   $236.70   $236.70  
  7 purchase totals = $752.64       $815.6345   $815.63   $815.55   $815.80