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 $172.82   13.615%   $196.3494   $196.35   $196.35   $196.30  
  Purchase #2 $47.97   8.518%   $52.0561   $52.06   $52.05   $52.10  
  Purchase #3 $212.58   5.477%   $224.223   $224.22   $224.20   $224.20  
  Purchase #4 $92.85   12.705%   $104.6466   $104.65   $104.65   $104.60  
  Purchase #5 $198.32   6.821%   $211.8474   $211.85   $211.85   $211.80  
  Purchase #6 $75.91   4.722%   $79.4945   $79.49   $79.50   $79.50  
  Purchase #7 $105.60   11.510%   $117.7546   $117.75   $117.75   $117.80  
  7 purchase totals = $906.05       $986.3716   $986.37   $986.35   $986.30