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 $85.53   3.102%   $88.1831   $88.18   $88.20   $88.20  
  Purchase #2 $201.59   11.411%   $224.5934   $224.59   $224.60   $224.60  
  Purchase #3 $65.29   9.242%   $71.3241   $71.32   $71.30   $71.30  
  Purchase #4 $180.30   9.763%   $197.9027   $197.90   $197.90   $197.90  
  Purchase #5 $70.42   6.849%   $75.2431   $75.24   $75.25   $75.20  
  Purchase #6 $239.28   6.153%   $254.0029   $254.00   $254.00   $254.00  
  Purchase #7 $68.81   8.689%   $74.7889   $74.79   $74.80   $74.80  
  7 purchase totals = $911.22       $986.0382   $986.02   $986.05   $986.00