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 $124.38   10.511%   $137.4536   $137.45   $137.45   $137.50  
  Purchase #2 $103.41   3.344%   $106.868   $106.87   $106.85   $106.90  
  Purchase #3 $250.27   5.613%   $264.3177   $264.32   $264.30   $264.30  
  Purchase #4 $78.49   5.703%   $82.9663   $82.97   $82.95   $83.00  
  Purchase #5 $208.80   4.836%   $218.8976   $218.90   $218.90   $218.90  
  Purchase #6 $131.97   11.124%   $146.6503   $146.65   $146.65   $146.70  
  Purchase #7 $213.68   5.710%   $225.8811   $225.88   $225.90   $225.90  
  7 purchase totals = $1,111.00       $1,183.0346   $1,183.04   $1,183.00   $1,183.20