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 $84.79   11.607%   $94.6316   $94.63   $94.65   $94.60  
  Purchase #2 $124.53   9.724%   $136.6393   $136.64   $136.65   $136.60  
  Purchase #3 $223.70   11.857%   $250.2241   $250.22   $250.20   $250.20  
  Purchase #4 $179.34   7.409%   $192.6273   $192.63   $192.65   $192.60  
  Purchase #5 $38.96   7.263%   $41.7897   $41.79   $41.80   $41.80  
  Purchase #6 $139.75   11.741%   $156.158   $156.16   $156.15   $156.20  
  Purchase #7 $49.25   8.767%   $53.5677   $53.57   $53.55   $53.60  
  7 purchase totals = $840.32       $925.6377   $925.64   $925.65   $925.60