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 $244.28   10.121%   $269.0036   $269.00   $269.00   $269.00  
  Purchase #2 $168.48   8.387%   $182.6104   $182.61   $182.60   $182.60  
  Purchase #3 $82.40   5.608%   $87.021   $87.02   $87.00   $87.00  
  Purchase #4 $200.70   7.651%   $216.0556   $216.06   $216.05   $216.10  
  Purchase #5 $10.93   9.780%   $11.999   $12.00   $12.00   $12.00  
  Purchase #6 $130.28   6.119%   $138.2518   $138.25   $138.25   $138.30  
  Purchase #7 $78.29   4.224%   $81.597   $81.60   $81.60   $81.60  
  7 purchase totals = $915.36       $986.5384   $986.54   $986.50   $986.60