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 $61.69   13.681%   $70.1298   $70.13   $70.15   $70.10  
  Purchase #2 $117.26   12.336%   $131.7252   $131.73   $131.75   $131.70  
  Purchase #3 $29.44   7.439%   $31.63   $31.63   $31.65   $31.60  
  Purchase #4 $200.68   10.742%   $222.237   $222.24   $222.25   $222.20  
  Purchase #5 $192.91   4.744%   $202.0617   $202.06   $202.05   $202.10  
  Purchase #6 $226.81   9.476%   $248.3025   $248.30   $248.30   $248.30  
  Purchase #7 $58.77   3.854%   $61.035   $61.04   $61.05   $61.00  
  7 purchase totals = $887.56       $967.1212   $967.13   $967.20   $967.00