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 $87.71   11.805%   $98.0642   $98.06   $98.05   $98.10  
  Purchase #2 $108.52   6.838%   $115.9406   $115.94   $115.95   $115.90  
  Purchase #3 $114.99   10.212%   $126.7328   $126.73   $126.75   $126.70  
  Purchase #4 $145.91   5.195%   $153.49   $153.49   $153.50   $153.50  
  Purchase #5 $119.85   7.657%   $129.0269   $129.03   $129.05   $129.00  
  Purchase #6 $158.98   11.375%   $177.064   $177.06   $177.05   $177.10  
  Purchase #7 $90.54   8.797%   $98.5048   $98.50   $98.50   $98.50  
  7 purchase totals = $826.50       $898.8233   $898.81   $898.85   $898.80