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 $175.82   10.543%   $194.3567   $194.36   $194.35   $194.40  
  Purchase #2 $236.44   11.121%   $262.7345   $262.73   $262.75   $262.70  
  Purchase #3 $157.25   3.555%   $162.8402   $162.84   $162.85   $162.80  
  Purchase #4 $240.54   10.278%   $265.2627   $265.26   $265.25   $265.30  
  Purchase #5 $67.84   3.452%   $70.1818   $70.18   $70.20   $70.20  
  Purchase #6 $49.64   8.335%   $53.7775   $53.78   $53.80   $53.80  
  Purchase #7 $236.33   6.322%   $251.2708   $251.27   $251.25   $251.30  
  7 purchase totals = $1,163.86       $1,260.4242   $1,260.42   $1,260.45   $1,260.50