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 $232.28   6.167%   $246.6047   $246.60   $246.60   $246.60  
  Purchase #2 $206.83   7.581%   $222.5098   $222.51   $222.50   $222.50  
  Purchase #3 $153.51   8.689%   $166.8485   $166.85   $166.85   $166.80  
  Purchase #4 $107.42   5.656%   $113.4957   $113.50   $113.50   $113.50  
  Purchase #5 $200.83   3.854%   $208.57   $208.57   $208.55   $208.60  
  Purchase #6 $10.58   10.338%   $11.6738   $11.67   $11.65   $11.70  
  Purchase #7 $205.60   8.714%   $223.516   $223.52   $223.50   $223.50  
  7 purchase totals = $1,117.05       $1,193.2185   $1,193.22   $1,193.15   $1,193.20