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 $118.99   13.126%   $134.6086   $134.61   $134.60   $134.60  
  Purchase #2 $239.52   11.427%   $266.89   $266.89   $266.90   $266.90  
  Purchase #3 $12.30   7.847%   $13.2652   $13.27   $13.25   $13.30  
  Purchase #4 $157.47   11.208%   $175.1192   $175.12   $175.10   $175.10  
  Purchase #5 $49.72   10.228%   $54.8054   $54.81   $54.80   $54.80  
  Purchase #6 $110.68   5.353%   $116.6047   $116.60   $116.60   $116.60  
  Purchase #7 $70.25   4.848%   $73.6557   $73.66   $73.65   $73.70  
  7 purchase totals = $758.93       $834.9488   $834.96   $834.90   $835.00