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 $49.83   5.643%   $52.6419   $52.64   $52.65   $52.60  
  Purchase #2 $249.42   6.723%   $266.1885   $266.19   $266.20   $266.20  
  Purchase #3 $176.32   5.351%   $185.7549   $185.75   $185.75   $185.80  
  Purchase #4 $187.33   4.445%   $195.6568   $195.66   $195.65   $195.70  
  Purchase #5 $161.72   10.329%   $178.4241   $178.42   $178.40   $178.40  
  Purchase #6 $64.69   10.423%   $71.4326   $71.43   $71.45   $71.40  
  Purchase #7 $58.75   11.511%   $65.5127   $65.51   $65.50   $65.50  
  7 purchase totals = $948.06       $1,015.6115   $1,015.60   $1,015.60   $1,015.60