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 $229.46   11.465%   $255.7676   $255.77   $255.75   $255.80  
  Purchase #2 $234.90   8.254%   $254.2886   $254.29   $254.30   $254.30  
  Purchase #3 $21.47   13.686%   $24.4084   $24.41   $24.40   $24.40  
  Purchase #4 $65.51   11.856%   $73.2769   $73.28   $73.30   $73.30  
  Purchase #5 $79.78   3.554%   $82.6154   $82.62   $82.60   $82.60  
  Purchase #6 $222.38   10.659%   $246.0835   $246.08   $246.10   $246.10  
  Purchase #7 $81.98   6.559%   $87.3571   $87.36   $87.35   $87.40  
  7 purchase totals = $935.48       $1,023.7975   $1,023.81   $1,023.80   $1,023.90