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 $24.68   7.103%   $26.433   $26.43   $26.45   $26.40  
  Purchase #2 $214.30   5.631%   $226.3672   $226.37   $226.35   $226.40  
  Purchase #3 $43.99   9.821%   $48.3103   $48.31   $48.30   $48.30  
  Purchase #4 $226.63   5.608%   $239.3394   $239.34   $239.35   $239.30  
  Purchase #5 $140.84   7.298%   $151.1185   $151.12   $151.10   $151.10  
  Purchase #6 $85.84   5.129%   $90.2427   $90.24   $90.25   $90.20  
  Purchase #7 $234.41   3.256%   $242.0424   $242.04   $242.05   $242.00  
  7 purchase totals = $970.69       $1,023.8535   $1,023.85   $1,023.85   $1,023.70