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 $179.79   13.506%   $204.0724   $204.07   $204.05   $204.10  
  Purchase #2 $208.93   12.582%   $235.2176   $235.22   $235.20   $235.20  
  Purchase #3 $67.78   12.289%   $76.1095   $76.11   $76.10   $76.10  
  Purchase #4 $207.26   3.532%   $214.5804   $214.58   $214.60   $214.60  
  Purchase #5 $133.63   6.131%   $141.8229   $141.82   $141.80   $141.80  
  Purchase #6 $197.71   8.750%   $215.0096   $215.01   $215.00   $215.00  
  Purchase #7 $211.78   12.794%   $238.8751   $238.88   $238.90   $238.90  
  7 purchase totals = $1,206.88       $1,325.6875   $1,325.69   $1,325.65   $1,325.70