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 $207.93   13.226%   $235.4308   $235.43   $235.45   $235.40  
  Purchase #2 $157.84   11.517%   $176.0184   $176.02   $176.00   $176.00  
  Purchase #3 $13.57   11.307%   $15.1044   $15.10   $15.10   $15.10  
  Purchase #4 $47.96   8.781%   $52.1714   $52.17   $52.15   $52.20  
  Purchase #5 $32.42   10.234%   $35.7379   $35.74   $35.75   $35.70  
  Purchase #6 $122.65   3.488%   $126.928   $126.93   $126.95   $126.90  
  Purchase #7 $49.54   10.459%   $54.7214   $54.72   $54.70   $54.70  
  7 purchase totals = $631.91       $696.1123   $696.11   $696.10   $696.00