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 $46.96   12.483%   $52.822   $52.82   $52.80   $52.80  
  Purchase #2 $19.93   4.874%   $20.9014   $20.90   $20.90   $20.90  
  Purchase #3 $42.82   10.104%   $47.1465   $47.15   $47.15   $47.10  
  Purchase #4 $95.35   3.383%   $98.5757   $98.58   $98.60   $98.60  
  Purchase #5 $41.66   6.354%   $44.3071   $44.31   $44.30   $44.30  
  Purchase #6 $156.61   8.564%   $170.0221   $170.02   $170.00   $170.00  
  Purchase #7 $77.41   4.383%   $80.8029   $80.80   $80.80   $80.80  
  7 purchase totals = $480.74       $514.5777   $514.58   $514.55   $514.50