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 $35.54   13.787%   $40.4399   $40.44   $40.45   $40.40  
  Purchase #2 $207.87   8.395%   $225.3207   $225.32   $225.30   $225.30  
  Purchase #3 $109.34   6.826%   $116.8035   $116.80   $116.80   $116.80  
  Purchase #4 $204.87   4.223%   $213.5217   $213.52   $213.50   $213.50  
  Purchase #5 $71.52   11.618%   $79.8292   $79.83   $79.85   $79.80  
  Purchase #6 $40.66   9.368%   $44.469   $44.47   $44.45   $44.50  
  Purchase #7 $11.26   7.854%   $12.1444   $12.14   $12.15   $12.10  
  7 purchase totals = $681.06       $732.5284   $732.52   $732.50   $732.40