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 $244.97   9.652%   $268.6145   $268.61   $268.60   $268.60  
  Purchase #2 $84.27   10.344%   $92.9869   $92.99   $93.00   $93.00  
  Purchase #3 $151.72   13.481%   $172.1734   $172.17   $172.15   $172.20  
  Purchase #4 $215.98   8.193%   $233.6752   $233.68   $233.70   $233.70  
  Purchase #5 $118.74   4.828%   $124.4728   $124.47   $124.45   $124.50  
  Purchase #6 $176.95   8.246%   $191.5413   $191.54   $191.55   $191.50  
  Purchase #7 $123.96   8.410%   $134.385   $134.39   $134.40   $134.40  
  7 purchase totals = $1,116.59       $1,217.8491   $1,217.85   $1,217.85   $1,217.90