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 $59.59   10.106%   $65.6122   $65.61   $65.60   $65.60  
  Purchase #2 $133.88   3.694%   $138.8255   $138.83   $138.85   $138.80  
  Purchase #3 $109.33   8.149%   $118.2393   $118.24   $118.25   $118.20  
  Purchase #4 $105.42   13.300%   $119.4409   $119.44   $119.45   $119.40  
  Purchase #5 $33.32   7.828%   $35.9283   $35.93   $35.95   $35.90  
  Purchase #6 $197.53   9.137%   $215.5783   $215.58   $215.60   $215.60  
  Purchase #7 $61.97   3.251%   $63.9846   $63.98   $64.00   $64.00  
  7 purchase totals = $701.04       $757.6091   $757.61   $757.70   $757.50