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 $203.93   11.106%   $226.5785   $226.58   $226.60   $226.60  
  Purchase #2 $219.50   9.347%   $240.0167   $240.02   $240.00   $240.00  
  Purchase #3 $34.81   9.512%   $38.1211   $38.12   $38.10   $38.10  
  Purchase #4 $94.75   12.544%   $106.6354   $106.64   $106.65   $106.60  
  Purchase #5 $50.99   10.282%   $56.2328   $56.23   $56.25   $56.20  
  Purchase #6 $40.76   8.360%   $44.1675   $44.17   $44.15   $44.20  
  Purchase #7 $202.71   5.599%   $214.0597   $214.06   $214.05   $214.10  
  7 purchase totals = $847.45       $925.8117   $925.82   $925.80   $925.80