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 $9.65   10.667%   $10.6794   $10.68   $10.70   $10.70  
  Purchase #2 $13.72   7.458%   $14.7432   $14.74   $14.75   $14.70  
  Purchase #3 $74.68   5.239%   $78.5925   $78.59   $78.60   $78.60  
  Purchase #4 $152.68   13.863%   $173.846   $173.85   $173.85   $173.80  
  Purchase #5 $113.35   4.102%   $117.9996   $118.00   $118.00   $118.00  
  Purchase #6 $90.45   10.695%   $100.1236   $100.12   $100.10   $100.10  
  Purchase #7 $129.50   4.475%   $135.2951   $135.30   $135.30   $135.30  
  7 purchase totals = $584.03       $631.2794   $631.28   $631.30   $631.20