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 $212.47   9.694%   $233.0668   $233.07   $233.05   $233.10  
  Purchase #2 $10.66   3.563%   $11.0398   $11.04   $11.05   $11.00  
  Purchase #3 $211.58   4.102%   $220.259   $220.26   $220.25   $220.30  
  Purchase #4 $93.54   5.356%   $98.55   $98.55   $98.55   $98.60  
  Purchase #5 $111.32   9.776%   $122.2026   $122.20   $122.20   $122.20  
  Purchase #6 $60.26   13.605%   $68.4584   $68.46   $68.45   $68.50  
  Purchase #7 $123.93   13.194%   $140.2813   $140.28   $140.30   $140.30  
  7 purchase totals = $823.76       $893.8579   $893.86   $893.85   $894.00