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 $234.63   3.226%   $242.1992   $242.20   $242.20   $242.20  
  Purchase #2 $25.93   6.311%   $27.5664   $27.57   $27.55   $27.60  
  Purchase #3 $223.89   6.574%   $238.6085   $238.61   $238.60   $238.60  
  Purchase #4 $53.70   7.467%   $57.7098   $57.71   $57.70   $57.70  
  Purchase #5 $192.61   13.626%   $218.855   $218.86   $218.85   $218.90  
  Purchase #6 $178.42   13.658%   $202.7886   $202.79   $202.80   $202.80  
  Purchase #7 $186.76   13.606%   $212.1706   $212.17   $212.15   $212.20  
  7 purchase totals = $1,095.94       $1,199.8981   $1,199.91   $1,199.85   $1,200.00