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 $189.58   9.716%   $207.9996   $208.00   $208.00   $208.00  
  Purchase #2 $95.54   8.613%   $103.7689   $103.77   $103.75   $103.80  
  Purchase #3 $20.31   6.473%   $21.6247   $21.62   $21.60   $21.60  
  Purchase #4 $242.63   8.165%   $262.4407   $262.44   $262.45   $262.40  
  Purchase #5 $227.84   11.424%   $253.8684   $253.87   $253.85   $253.90  
  Purchase #6 $27.50   9.380%   $30.0795   $30.08   $30.10   $30.10  
  Purchase #7 $133.71   5.287%   $140.7792   $140.78   $140.80   $140.80  
  7 purchase totals = $937.11       $1,020.5610   $1,020.56   $1,020.55   $1,020.60