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 $62.58   5.506%   $66.0257   $66.03   $66.05   $66.00  
  Purchase #2 $227.85   13.796%   $259.2842   $259.28   $259.30   $259.30  
  Purchase #3 $82.95   4.504%   $86.6861   $86.69   $86.70   $86.70  
  Purchase #4 $210.86   12.764%   $237.7742   $237.77   $237.75   $237.80  
  Purchase #5 $226.97   3.600%   $235.1409   $235.14   $235.15   $235.10  
  Purchase #6 $216.49   10.686%   $239.6241   $239.62   $239.60   $239.60  
  Purchase #7 $153.82   11.570%   $171.617   $171.62   $171.60   $171.60  
  7 purchase totals = $1,181.52       $1,296.1522   $1,296.15   $1,296.15   $1,296.10