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 $229.96   5.109%   $241.7087   $241.71   $241.70   $241.70  
  Purchase #2 $152.97   5.629%   $161.5807   $161.58   $161.60   $161.60  
  Purchase #3 $32.81   12.221%   $36.8197   $36.82   $36.80   $36.80  
  Purchase #4 $87.98   8.606%   $95.5516   $95.55   $95.55   $95.60  
  Purchase #5 $61.99   11.665%   $69.2211   $69.22   $69.20   $69.20  
  Purchase #6 $93.51   11.855%   $104.5956   $104.60   $104.60   $104.60  
  Purchase #7 $224.71   12.512%   $252.8257   $252.83   $252.85   $252.80  
  7 purchase totals = $883.93       $962.3031   $962.31   $962.30   $962.30