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 $13.63   6.771%   $14.5529   $14.55   $14.55   $14.60  
  Purchase #2 $213.36   10.610%   $235.9975   $236.00   $236.00   $236.00  
  Purchase #3 $65.74   3.209%   $67.8496   $67.85   $67.85   $67.80  
  Purchase #4 $130.93   5.742%   $138.448   $138.45   $138.45   $138.40  
  Purchase #5 $98.45   7.174%   $105.5128   $105.51   $105.50   $105.50  
  Purchase #6 $195.63   11.557%   $218.239   $218.24   $218.25   $218.20  
  Purchase #7 $112.34   13.506%   $127.5126   $127.51   $127.50   $127.50  
  7 purchase totals = $830.08       $908.1124   $908.11   $908.10   $908.00