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 $235.83   10.367%   $260.2785   $260.28   $260.30   $260.30  
  Purchase #2 $207.81   5.639%   $219.5284   $219.53   $219.55   $219.50  
  Purchase #3 $49.85   9.788%   $54.7293   $54.73   $54.75   $54.70  
  Purchase #4 $237.43   10.756%   $262.968   $262.97   $262.95   $263.00  
  Purchase #5 $181.76   10.278%   $200.4413   $200.44   $200.45   $200.40  
  Purchase #6 $162.90   4.671%   $170.5091   $170.51   $170.50   $170.50  
  Purchase #7 $114.89   7.635%   $123.6619   $123.66   $123.65   $123.70  
  7 purchase totals = $1,190.47       $1,292.1165   $1,292.12   $1,292.15   $1,292.10