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 $52.71   13.697%   $59.9297   $59.93   $59.95   $59.90  
  Purchase #2 $111.25   8.445%   $120.6451   $120.65   $120.65   $120.60  
  Purchase #3 $66.99   11.630%   $74.7809   $74.78   $74.80   $74.80  
  Purchase #4 $181.50   6.592%   $193.4645   $193.46   $193.45   $193.50  
  Purchase #5 $222.75   12.439%   $250.4579   $250.46   $250.45   $250.50  
  Purchase #6 $44.58   5.448%   $47.0087   $47.01   $47.00   $47.00  
  Purchase #7 $67.88   11.373%   $75.6   $75.60   $75.60   $75.60  
  7 purchase totals = $747.66       $821.8868   $821.89   $821.90   $821.90