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 $140.66   8.759%   $152.9804   $152.98   $153.00   $153.00  
  Purchase #2 $162.81   8.395%   $176.4779   $176.48   $176.50   $176.50  
  Purchase #3 $206.40   5.259%   $217.2546   $217.25   $217.25   $217.30  
  Purchase #4 $13.52   11.176%   $15.031   $15.03   $15.05   $15.00  
  Purchase #5 $78.33   8.131%   $84.699   $84.70   $84.70   $84.70  
  Purchase #6 $218.97   4.239%   $228.2521   $228.25   $228.25   $228.30  
  Purchase #7 $224.80   6.208%   $238.7556   $238.76   $238.75   $238.80  
  7 purchase totals = $1,045.49       $1,113.4506   $1,113.45   $1,113.50   $1,113.60