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 $60.53   3.642%   $62.7345   $62.73   $62.75   $62.70  
  Purchase #2 $206.35   8.681%   $224.2632   $224.26   $224.25   $224.30  
  Purchase #3 $210.41   8.577%   $228.4569   $228.46   $228.45   $228.50  
  Purchase #4 $65.56   13.758%   $74.5797   $74.58   $74.60   $74.60  
  Purchase #5 $11.55   5.871%   $12.2281   $12.23   $12.25   $12.20  
  Purchase #6 $90.80   3.183%   $93.6902   $93.69   $93.70   $93.70  
  Purchase #7 $221.48   9.827%   $243.2448   $243.24   $243.25   $243.20  
  7 purchase totals = $866.68       $939.1974   $939.19   $939.25   $939.20