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   6.747%   $63.6105   $63.61   $63.60   $63.60  
  Purchase #2 $228.25   7.847%   $246.1608   $246.16   $246.15   $246.20  
  Purchase #3 $88.26   5.820%   $93.3967   $93.40   $93.40   $93.40  
  Purchase #4 $234.51   5.807%   $248.128   $248.13   $248.15   $248.10  
  Purchase #5 $192.84   8.206%   $208.6645   $208.66   $208.65   $208.70  
  Purchase #6 $143.28   12.426%   $161.084   $161.08   $161.10   $161.10  
  Purchase #7 $6.29   3.385%   $6.5029   $6.50   $6.50   $6.50  
  7 purchase totals = $953.02       $1,027.5474   $1,027.54   $1,027.55   $1,027.60