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 $141.63   12.547%   $159.4003   $159.40   $159.40   $159.40  
  Purchase #2 $24.51   7.104%   $26.2512   $26.25   $26.25   $26.30  
  Purchase #3 $248.60   8.614%   $270.0144   $270.01   $270.00   $270.00  
  Purchase #4 $68.63   11.261%   $76.3584   $76.36   $76.35   $76.40  
  Purchase #5 $211.60   5.391%   $223.0074   $223.01   $223.00   $223.00  
  Purchase #6 $232.36   11.366%   $258.77   $258.77   $258.75   $258.80  
  Purchase #7 $158.69   6.292%   $168.6748   $168.67   $168.65   $168.70  
  7 purchase totals = $1,086.02       $1,182.4765   $1,182.47   $1,182.40   $1,182.60