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 $240.94   6.226%   $255.9409   $255.94   $255.95   $255.90  
  Purchase #2 $246.70   12.563%   $277.6929   $277.69   $277.70   $277.70  
  Purchase #3 $34.57   4.744%   $36.21   $36.21   $36.20   $36.20  
  Purchase #4 $185.89   8.365%   $201.4397   $201.44   $201.45   $201.40  
  Purchase #5 $87.43   7.297%   $93.8098   $93.81   $93.80   $93.80  
  Purchase #6 $181.49   12.554%   $204.2743   $204.27   $204.25   $204.30  
  Purchase #7 $172.65   5.422%   $182.0111   $182.01   $182.00   $182.00  
  7 purchase totals = $1,149.67       $1,251.3787   $1,251.37   $1,251.35   $1,251.30