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 $67.41   9.313%   $73.6879   $73.69   $73.70   $73.70  
  Purchase #2 $248.28   10.687%   $274.8137   $274.81   $274.80   $274.80  
  Purchase #3 $222.59   3.128%   $229.5526   $229.55   $229.55   $229.60  
  Purchase #4 $86.30   4.568%   $90.2422   $90.24   $90.25   $90.20  
  Purchase #5 $250.29   8.643%   $271.9226   $271.92   $271.90   $271.90  
  Purchase #6 $206.25   9.129%   $225.0786   $225.08   $225.10   $225.10  
  Purchase #7 $209.65   13.486%   $237.9234   $237.92   $237.90   $237.90  
  7 purchase totals = $1,290.77       $1,403.2210   $1,403.21   $1,403.20   $1,403.20