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 $63.64   6.102%   $67.5233   $67.52   $67.50   $67.50  
  Purchase #2 $224.87   12.487%   $252.9495   $252.95   $252.95   $252.90  
  Purchase #3 $185.64   13.215%   $210.1723   $210.17   $210.15   $210.20  
  Purchase #4 $235.33   13.308%   $266.6477   $266.65   $266.65   $266.60  
  Purchase #5 $31.38   13.501%   $35.6166   $35.62   $35.60   $35.60  
  Purchase #6 $71.99   12.793%   $81.1997   $81.20   $81.20   $81.20  
  Purchase #7 $237.54   4.745%   $248.8113   $248.81   $248.80   $248.80  
  7 purchase totals = $1,050.39       $1,162.9204   $1,162.92   $1,162.85   $1,162.80