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 $202.83   11.762%   $226.6869   $226.69   $226.70   $226.70  
  Purchase #2 $185.92   8.840%   $202.3553   $202.36   $202.35   $202.40  
  Purchase #3 $184.47   7.609%   $198.5063   $198.51   $198.50   $198.50  
  Purchase #4 $65.33   3.606%   $67.6858   $67.69   $67.70   $67.70  
  Purchase #5 $57.85   4.249%   $60.308   $60.31   $60.30   $60.30  
  Purchase #6 $143.45   5.608%   $151.4947   $151.49   $151.50   $151.50  
  Purchase #7 $126.85   7.393%   $136.228   $136.23   $136.25   $136.20  
  7 purchase totals = $966.70       $1,043.2650   $1,043.28   $1,043.30   $1,043.30