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 $236.50   5.664%   $249.8954   $249.90   $249.90   $249.90  
  Purchase #2 $233.61   8.237%   $252.8525   $252.85   $252.85   $252.90  
  Purchase #3 $62.57   12.635%   $70.4757   $70.48   $70.50   $70.50  
  Purchase #4 $184.31   6.448%   $196.1943   $196.19   $196.20   $196.20  
  Purchase #5 $46.35   6.699%   $49.455   $49.46   $49.45   $49.50  
  Purchase #6 $82.25   6.159%   $87.3158   $87.32   $87.30   $87.30  
  Purchase #7 $48.60   5.428%   $51.238   $51.24   $51.25   $51.20  
  7 purchase totals = $894.19       $957.4267   $957.44   $957.45   $957.50