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 $249.84   9.670%   $273.9995   $274.00   $274.00   $274.00  
  Purchase #2 $161.26   13.626%   $183.2333   $183.23   $183.25   $183.20  
  Purchase #3 $206.90   7.542%   $222.5044   $222.50   $222.50   $222.50  
  Purchase #4 $212.38   11.490%   $236.7825   $236.78   $236.80   $236.80  
  Purchase #5 $8.29   11.628%   $9.254   $9.25   $9.25   $9.30  
  Purchase #6 $164.27   3.218%   $169.5562   $169.56   $169.55   $169.60  
  Purchase #7 $231.52   9.724%   $254.033   $254.03   $254.05   $254.00  
  7 purchase totals = $1,234.46       $1,349.3629   $1,349.35   $1,349.40   $1,349.40