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 $139.83   9.147%   $152.6203   $152.62   $152.60   $152.60  
  Purchase #2 $215.52   8.141%   $233.0655   $233.07   $233.05   $233.10  
  Purchase #3 $177.64   4.634%   $185.8718   $185.87   $185.85   $185.90  
  Purchase #4 $27.31   4.865%   $28.6386   $28.64   $28.65   $28.60  
  Purchase #5 $65.66   6.169%   $69.7106   $69.71   $69.70   $69.70  
  Purchase #6 $193.87   5.356%   $204.2537   $204.25   $204.25   $204.30  
  Purchase #7 $98.26   10.403%   $108.482   $108.48   $108.50   $108.50  
  7 purchase totals = $918.09       $982.6425   $982.64   $982.60   $982.70