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 $69.25   9.479%   $75.8142   $75.81   $75.80   $75.80  
  Purchase #2 $149.53   4.601%   $156.4099   $156.41   $156.40   $156.40  
  Purchase #3 $52.96   9.382%   $57.9287   $57.93   $57.95   $57.90  
  Purchase #4 $108.68   7.161%   $116.4626   $116.46   $116.45   $116.50  
  Purchase #5 $236.73   10.787%   $262.2661   $262.27   $262.25   $262.30  
  Purchase #6 $63.70   4.394%   $66.499   $66.50   $66.50   $66.50  
  Purchase #7 $173.50   6.162%   $184.1911   $184.19   $184.20   $184.20  
  7 purchase totals = $854.35       $919.5716   $919.57   $919.55   $919.60