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 $94.86   11.738%   $105.9947   $105.99   $106.00   $106.00  
  Purchase #2 $128.55   8.365%   $139.3032   $139.30   $139.30   $139.30  
  Purchase #3 $226.93   11.135%   $252.1987   $252.20   $252.20   $252.20  
  Purchase #4 $213.42   10.568%   $235.9742   $235.97   $235.95   $236.00  
  Purchase #5 $38.63   5.250%   $40.6581   $40.66   $40.65   $40.70  
  Purchase #6 $161.88   6.697%   $172.7211   $172.72   $172.70   $172.70  
  Purchase #7 $42.94   9.285%   $46.927   $46.93   $46.95   $46.90  
  7 purchase totals = $907.21       $993.7770   $993.77   $993.75   $993.80