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 $66.59   3.673%   $69.0359   $69.04   $69.05   $69.00  
  Purchase #2 $201.81   11.339%   $224.6932   $224.69   $224.70   $224.70  
  Purchase #3 $147.74   4.114%   $153.818   $153.82   $153.80   $153.80  
  Purchase #4 $90.77   8.119%   $98.1396   $98.14   $98.15   $98.10  
  Purchase #5 $30.54   3.463%   $31.5976   $31.60   $31.60   $31.60  
  Purchase #6 $98.30   5.777%   $103.9788   $103.98   $104.00   $104.00  
  Purchase #7 $62.55   13.487%   $70.9861   $70.99   $71.00   $71.00  
  7 purchase totals = $698.30       $752.2492   $752.26   $752.30   $752.20