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 $44.38   10.861%   $49.2001   $49.20   $49.20   $49.20  
  Purchase #2 $207.55   11.621%   $231.6694   $231.67   $231.65   $231.70  
  Purchase #3 $179.94   3.416%   $186.0868   $186.09   $186.10   $186.10  
  Purchase #4 $131.42   5.592%   $138.769   $138.77   $138.75   $138.80  
  Purchase #5 $68.46   6.814%   $73.1249   $73.12   $73.10   $73.10  
  Purchase #6 $190.39   7.320%   $204.3265   $204.33   $204.35   $204.30  
  Purchase #7 $78.91   8.511%   $85.626   $85.63   $85.65   $85.60  
  7 purchase totals = $901.05       $968.8027   $968.81   $968.80   $968.80