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 $60.30   3.713%   $62.5389   $62.54   $62.55   $62.50  
  Purchase #2 $84.46   3.670%   $87.5597   $87.56   $87.55   $87.60  
  Purchase #3 $249.28   13.118%   $281.9806   $281.98   $282.00   $282.00  
  Purchase #4 $158.75   10.394%   $175.2505   $175.25   $175.25   $175.30  
  Purchase #5 $68.65   10.685%   $75.9853   $75.99   $76.00   $76.00  
  Purchase #6 $45.49   8.287%   $49.2598   $49.26   $49.25   $49.30  
  Purchase #7 $196.94   4.651%   $206.0997   $206.10   $206.10   $206.10  
  7 purchase totals = $863.87       $938.6745   $938.68   $938.70   $938.80