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 $178.96   13.724%   $203.5205   $203.52   $203.50   $203.50  
  Purchase #2 $32.29   5.289%   $33.9978   $34.00   $34.00   $34.00  
  Purchase #3 $150.49   5.172%   $158.2733   $158.27   $158.25   $158.30  
  Purchase #4 $17.72   4.215%   $18.4669   $18.47   $18.45   $18.50  
  Purchase #5 $227.31   8.486%   $246.5995   $246.60   $246.60   $246.60  
  Purchase #6 $154.37   5.341%   $162.6149   $162.61   $162.60   $162.60  
  Purchase #7 $146.99   11.706%   $164.1966   $164.20   $164.20   $164.20  
  7 purchase totals = $908.13       $987.6695   $987.67   $987.60   $987.70