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 $106.34   12.795%   $119.9462   $119.95   $119.95   $119.90  
  Purchase #2 $161.81   7.714%   $174.292   $174.29   $174.30   $174.30  
  Purchase #3 $228.69   13.595%   $259.7804   $259.78   $259.80   $259.80  
  Purchase #4 $68.35   13.553%   $77.6135   $77.61   $77.60   $77.60  
  Purchase #5 $200.91   8.607%   $218.2023   $218.20   $218.20   $218.20  
  Purchase #6 $36.25   11.663%   $40.4778   $40.48   $40.50   $40.50  
  Purchase #7 $108.77   12.568%   $122.4402   $122.44   $122.45   $122.40  
  7 purchase totals = $911.12       $1,012.7524   $1,012.75   $1,012.80   $1,012.70