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 $242.98   4.194%   $253.1706   $253.17   $253.15   $253.20  
  Purchase #2 $232.46   3.535%   $240.6775   $240.68   $240.70   $240.70  
  Purchase #3 $70.68   4.154%   $73.616   $73.62   $73.60   $73.60  
  Purchase #4 $58.26   8.296%   $63.0932   $63.09   $63.10   $63.10  
  Purchase #5 $41.50   3.138%   $42.8023   $42.80   $42.80   $42.80  
  Purchase #6 $155.84   5.239%   $164.0045   $164.00   $164.00   $164.00  
  Purchase #7 $233.33   6.194%   $247.7825   $247.78   $247.80   $247.80  
  7 purchase totals = $1,035.05       $1,085.1466   $1,085.14   $1,085.15   $1,085.20