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 $234.77   11.395%   $261.522   $261.52   $261.50   $261.50  
  Purchase #2 $183.52   4.836%   $192.395   $192.40   $192.40   $192.40  
  Purchase #3 $248.41   7.498%   $267.0358   $267.04   $267.05   $267.00  
  Purchase #4 $70.60   5.192%   $74.2656   $74.27   $74.25   $74.30  
  Purchase #5 $212.88   12.644%   $239.7965   $239.80   $239.80   $239.80  
  Purchase #6 $108.54   9.693%   $119.0608   $119.06   $119.05   $119.10  
  Purchase #7 $92.40   4.416%   $96.4804   $96.48   $96.50   $96.50  
  7 purchase totals = $1,151.12       $1,250.5561   $1,250.57   $1,250.55   $1,250.60