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 $186.88   8.423%   $202.6209   $202.62   $202.60   $202.60  
  Purchase #2 $231.92   8.574%   $251.8048   $251.80   $251.80   $251.80  
  Purchase #3 $227.77   5.439%   $240.1584   $240.16   $240.15   $240.20  
  Purchase #4 $163.66   5.506%   $172.6711   $172.67   $172.65   $172.70  
  Purchase #5 $235.57   7.420%   $253.0493   $253.05   $253.05   $253.00  
  Purchase #6 $124.86   9.417%   $136.6181   $136.62   $136.60   $136.60  
  Purchase #7 $5.26   8.631%   $5.714   $5.71   $5.70   $5.70  
  7 purchase totals = $1,175.92       $1,262.6366   $1,262.63   $1,262.55   $1,262.60