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 $221.93   8.572%   $240.9538   $240.95   $240.95   $241.00  
  Purchase #2 $152.95   13.865%   $174.1565   $174.16   $174.15   $174.20  
  Purchase #3 $63.87   6.289%   $67.8868   $67.89   $67.90   $67.90  
  Purchase #4 $130.31   12.493%   $146.5896   $146.59   $146.60   $146.60  
  Purchase #5 $22.86   8.794%   $24.8703   $24.87   $24.85   $24.90  
  Purchase #6 $215.72   12.592%   $242.8835   $242.88   $242.90   $242.90  
  Purchase #7 $184.55   10.567%   $204.0514   $204.05   $204.05   $204.10  
  7 purchase totals = $992.19       $1,101.3919   $1,101.39   $1,101.40   $1,101.60