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 $214.52   10.347%   $236.7164   $236.72   $236.70   $236.70  
  Purchase #2 $154.74   5.691%   $163.5463   $163.55   $163.55   $163.50  
  Purchase #3 $226.37   11.678%   $252.8055   $252.81   $252.80   $252.80  
  Purchase #4 $19.69   5.426%   $20.7584   $20.76   $20.75   $20.80  
  Purchase #5 $133.40   8.325%   $144.5056   $144.51   $144.50   $144.50  
  Purchase #6 $224.89   9.457%   $246.1578   $246.16   $246.15   $246.20  
  Purchase #7 $182.28   11.425%   $203.1055   $203.11   $203.10   $203.10  
  7 purchase totals = $1,155.89       $1,267.5955   $1,267.62   $1,267.55   $1,267.60