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 $186.48   9.266%   $203.7592   $203.76   $203.75   $203.80  
  Purchase #2 $206.30   5.262%   $217.1555   $217.16   $217.15   $217.20  
  Purchase #3 $96.48   10.472%   $106.5834   $106.58   $106.60   $106.60  
  Purchase #4 $186.77   11.615%   $208.4633   $208.46   $208.45   $208.50  
  Purchase #5 $78.94   5.821%   $83.5351   $83.54   $83.55   $83.50  
  Purchase #6 $108.75   9.678%   $119.2748   $119.27   $119.25   $119.30  
  Purchase #7 $106.94   9.767%   $117.3848   $117.38   $117.40   $117.40  
  7 purchase totals = $970.66       $1,056.1561   $1,056.15   $1,056.15   $1,056.30