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 $223.88   10.153%   $246.6105   $246.61   $246.60   $246.60  
  Purchase #2 $60.37   4.765%   $63.2466   $63.25   $63.25   $63.20  
  Purchase #3 $168.95   9.388%   $184.811   $184.81   $184.80   $184.80  
  Purchase #4 $196.58   8.209%   $212.7173   $212.72   $212.70   $212.70  
  Purchase #5 $201.60   10.195%   $222.1531   $222.15   $222.15   $222.20  
  Purchase #6 $65.96   8.295%   $71.4314   $71.43   $71.45   $71.40  
  Purchase #7 $16.84   10.736%   $18.6479   $18.65   $18.65   $18.60  
  7 purchase totals = $934.18       $1,019.6178   $1,019.62   $1,019.60   $1,019.50