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 $36.40   11.560%   $40.6078   $40.61   $40.60   $40.60  
  Purchase #2 $207.82   4.858%   $217.9159   $217.92   $217.90   $217.90  
  Purchase #3 $141.64   13.814%   $161.2061   $161.21   $161.20   $161.20  
  Purchase #4 $214.62   13.132%   $242.8039   $242.80   $242.80   $242.80  
  Purchase #5 $207.30   7.241%   $222.3106   $222.31   $222.30   $222.30  
  Purchase #6 $61.90   11.837%   $69.2271   $69.23   $69.25   $69.20  
  Purchase #7 $174.83   13.691%   $198.766   $198.77   $198.75   $198.80  
  7 purchase totals = $1,044.51       $1,152.8374   $1,152.85   $1,152.80   $1,152.80