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 $239.83   6.187%   $254.6683   $254.67   $254.65   $254.70  
  Purchase #2 $192.31   7.448%   $206.6332   $206.63   $206.65   $206.60  
  Purchase #3 $123.32   13.423%   $139.8732   $139.87   $139.85   $139.90  
  Purchase #4 $158.52   6.286%   $168.4846   $168.48   $168.50   $168.50  
  Purchase #5 $44.65   3.354%   $46.1476   $46.15   $46.15   $46.10  
  Purchase #6 $213.56   5.848%   $226.049   $226.05   $226.05   $226.00  
  Purchase #7 $239.93   6.463%   $255.4367   $255.44   $255.45   $255.40  
  7 purchase totals = $1,212.12       $1,297.2926   $1,297.29   $1,297.30   $1,297.20