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 $63.48   4.541%   $66.3626   $66.36   $66.35   $66.40  
  Purchase #2 $163.90   13.851%   $186.6018   $186.60   $186.60   $186.60  
  Purchase #3 $141.49   8.180%   $153.0639   $153.06   $153.05   $153.10  
  Purchase #4 $119.95   13.356%   $135.9705   $135.97   $135.95   $136.00  
  Purchase #5 $178.78   13.676%   $203.23   $203.23   $203.25   $203.20  
  Purchase #6 $71.61   3.426%   $74.0634   $74.06   $74.05   $74.10  
  Purchase #7 $218.92   10.834%   $242.6378   $242.64   $242.65   $242.60  
  7 purchase totals = $958.13       $1,061.9300   $1,061.92   $1,061.90   $1,062.00