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 $232.56   5.752%   $245.9369   $245.94   $245.95   $245.90  
  Purchase #2 $87.83   9.172%   $95.8858   $95.89   $95.90   $95.90  
  Purchase #3 $233.64   8.713%   $253.9971   $254.00   $254.00   $254.00  
  Purchase #4 $77.59   8.538%   $84.2146   $84.21   $84.20   $84.20  
  Purchase #5 $134.25   5.698%   $141.8996   $141.90   $141.90   $141.90  
  Purchase #6 $78.66   4.658%   $82.324   $82.32   $82.30   $82.30  
  Purchase #7 $43.54   9.650%   $47.7416   $47.74   $47.75   $47.70  
  7 purchase totals = $888.07       $951.9996   $952.00   $952.00   $951.90