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 $107.93   8.483%   $117.0857   $117.09   $117.10   $117.10  
  Purchase #2 $156.79   9.665%   $171.9438   $171.94   $171.95   $171.90  
  Purchase #3 $48.91   13.856%   $55.687   $55.69   $55.70   $55.70  
  Purchase #4 $223.85   8.530%   $242.9444   $242.94   $242.95   $242.90  
  Purchase #5 $64.61   11.155%   $71.8172   $71.82   $71.80   $71.80  
  Purchase #6 $182.83   5.277%   $192.4779   $192.48   $192.50   $192.50  
  Purchase #7 $192.27   9.437%   $210.4145   $210.41   $210.40   $210.40  
  7 purchase totals = $977.19       $1,062.3705   $1,062.37   $1,062.40   $1,062.30