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 $52.80   8.788%   $57.4401   $57.44   $57.45   $57.40  
  Purchase #2 $232.91   6.189%   $247.3248   $247.32   $247.30   $247.30  
  Purchase #3 $159.76   10.712%   $176.8735   $176.87   $176.85   $176.90  
  Purchase #4 $139.36   11.687%   $155.647   $155.65   $155.65   $155.60  
  Purchase #5 $161.92   9.125%   $176.6952   $176.70   $176.70   $176.70  
  Purchase #6 $59.26   12.354%   $66.581   $66.58   $66.60   $66.60  
  Purchase #7 $218.93   4.622%   $229.0489   $229.05   $229.05   $229.00  
  7 purchase totals = $1,024.94       $1,109.6105   $1,109.61   $1,109.60   $1,109.50