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 $231.42   6.742%   $247.0223   $247.02   $247.00   $247.00  
  Purchase #2 $79.73   8.133%   $86.2144   $86.21   $86.20   $86.20  
  Purchase #3 $207.35   7.175%   $222.2274   $222.23   $222.25   $222.20  
  Purchase #4 $43.96   5.771%   $46.4969   $46.50   $46.50   $46.50  
  Purchase #5 $179.61   9.506%   $196.6837   $196.68   $196.70   $196.70  
  Purchase #6 $95.58   11.389%   $106.4656   $106.47   $106.45   $106.50  
  Purchase #7 $86.47   4.675%   $90.5125   $90.51   $90.50   $90.50  
  7 purchase totals = $924.12       $995.6228   $995.62   $995.60   $995.60