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 $239.84   9.643%   $262.9678   $262.97   $262.95   $263.00  
  Purchase #2 $218.95   7.522%   $235.4194   $235.42   $235.40   $235.40  
  Purchase #3 $153.93   11.400%   $171.478   $171.48   $171.50   $171.50  
  Purchase #4 $47.95   12.562%   $53.9735   $53.97   $53.95   $54.00  
  Purchase #5 $51.39   12.547%   $57.8379   $57.84   $57.85   $57.80  
  Purchase #6 $34.78   8.410%   $37.705   $37.71   $37.70   $37.70  
  Purchase #7 $154.44   13.393%   $175.1241   $175.12   $175.10   $175.10  
  7 purchase totals = $901.28       $994.5057   $994.51   $994.45   $994.50