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 $239.25   12.425%   $268.9768   $268.98   $269.00   $269.00  
  Purchase #2 $182.54   7.844%   $196.8584   $196.86   $196.85   $196.90  
  Purchase #3 $52.74   6.267%   $56.0452   $56.05   $56.05   $56.00  
  Purchase #4 $100.82   5.364%   $106.228   $106.23   $106.25   $106.20  
  Purchase #5 $32.83   6.527%   $34.9728   $34.97   $34.95   $35.00  
  Purchase #6 $217.87   4.352%   $227.3517   $227.35   $227.35   $227.40  
  Purchase #7 $121.37   12.175%   $136.1468   $136.15   $136.15   $136.10  
  7 purchase totals = $947.42       $1,026.5797   $1,026.59   $1,026.60   $1,026.60