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 $220.39   4.325%   $229.9219   $229.92   $229.90   $229.90  
  Purchase #2 $170.39   11.737%   $190.3887   $190.39   $190.40   $190.40  
  Purchase #3 $137.84   7.443%   $148.0994   $148.10   $148.10   $148.10  
  Purchase #4 $155.55   12.857%   $175.5491   $175.55   $175.55   $175.50  
  Purchase #5 $128.57   12.112%   $144.1424   $144.14   $144.15   $144.10  
  Purchase #6 $157.71   3.623%   $163.4238   $163.42   $163.40   $163.40  
  Purchase #7 $222.81   6.320%   $236.8916   $236.89   $236.90   $236.90  
  7 purchase totals = $1,193.26       $1,288.4169   $1,288.41   $1,288.40   $1,288.30