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 $124.68   8.486%   $135.2603   $135.26   $135.25   $135.30  
  Purchase #2 $204.82   11.623%   $228.6262   $228.63   $228.65   $228.60  
  Purchase #3 $187.83   10.857%   $208.2227   $208.22   $208.20   $208.20  
  Purchase #4 $78.55   9.170%   $85.753   $85.75   $85.75   $85.80  
  Purchase #5 $139.37   8.619%   $151.3823   $151.38   $151.40   $151.40  
  Purchase #6 $163.26   8.792%   $177.6138   $177.61   $177.60   $177.60  
  Purchase #7 $143.28   10.522%   $158.3559   $158.36   $158.35   $158.40  
  7 purchase totals = $1,041.79       $1,145.2142   $1,145.21   $1,145.20   $1,145.30