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 $211.41   11.346%   $235.3966   $235.40   $235.40   $235.40  
  Purchase #2 $220.70   11.439%   $245.9459   $245.95   $245.95   $245.90  
  Purchase #3 $149.76   12.297%   $168.176   $168.18   $168.20   $168.20  
  Purchase #4 $47.41   13.672%   $53.8919   $53.89   $53.90   $53.90  
  Purchase #5 $227.50   11.236%   $253.0619   $253.06   $253.05   $253.10  
  Purchase #6 $31.69   12.410%   $35.6227   $35.62   $35.60   $35.60  
  Purchase #7 $28.37   13.752%   $32.2714   $32.27   $32.25   $32.30  
  7 purchase totals = $916.84       $1,024.3664   $1,024.37   $1,024.35   $1,024.40