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 $159.79   10.725%   $176.9275   $176.93   $176.95   $176.90  
  Purchase #2 $48.45   12.133%   $54.3284   $54.33   $54.35   $54.30  
  Purchase #3 $39.89   11.827%   $44.6078   $44.61   $44.60   $44.60  
  Purchase #4 $8.83   12.416%   $9.9263   $9.93   $9.95   $9.90  
  Purchase #5 $92.81   6.195%   $98.5596   $98.56   $98.55   $98.60  
  Purchase #6 $61.40   5.414%   $64.7242   $64.72   $64.70   $64.70  
  Purchase #7 $142.49   6.681%   $152.0098   $152.01   $152.00   $152.00  
  7 purchase totals = $553.66       $601.0836   $601.09   $601.10   $601.00