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 $211.87   7.413%   $227.5759   $227.58   $227.60   $227.60  
  Purchase #2 $141.45   10.735%   $156.6347   $156.63   $156.65   $156.60  
  Purchase #3 $174.65   8.840%   $190.0891   $190.09   $190.10   $190.10  
  Purchase #4 $246.66   7.746%   $265.7663   $265.77   $265.75   $265.80  
  Purchase #5 $182.37   12.688%   $205.5091   $205.51   $205.50   $205.50  
  Purchase #6 $61.63   5.498%   $65.0184   $65.02   $65.00   $65.00  
  Purchase #7 $229.26   5.319%   $241.4543   $241.45   $241.45   $241.50  
  7 purchase totals = $1,247.89       $1,352.0478   $1,352.05   $1,352.05   $1,352.10