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 $179.58   13.699%   $204.1807   $204.18   $204.20   $204.20  
  Purchase #2 $174.51   13.210%   $197.5628   $197.56   $197.55   $197.60  
  Purchase #3 $230.49   3.796%   $239.2394   $239.24   $239.25   $239.20  
  Purchase #4 $66.42   5.583%   $70.1282   $70.13   $70.15   $70.10  
  Purchase #5 $85.59   8.748%   $93.0774   $93.08   $93.10   $93.10  
  Purchase #6 $44.58   6.492%   $47.4741   $47.47   $47.45   $47.50  
  Purchase #7 $195.86   6.653%   $208.8906   $208.89   $208.90   $208.90  
  7 purchase totals = $977.03       $1,060.5532   $1,060.55   $1,060.60   $1,060.60