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 $217.67   6.566%   $231.9622   $231.96   $231.95   $232.00  
  Purchase #2 $207.78   13.119%   $235.0387   $235.04   $235.05   $235.00  
  Purchase #3 $92.25   10.393%   $101.8375   $101.84   $101.85   $101.80  
  Purchase #4 $214.59   11.466%   $239.1949   $239.19   $239.20   $239.20  
  Purchase #5 $7.42   9.862%   $8.1518   $8.15   $8.15   $8.20  
  Purchase #6 $168.62   11.649%   $188.2625   $188.26   $188.25   $188.30  
  Purchase #7 $25.89   5.691%   $27.3634   $27.36   $27.35   $27.40  
  7 purchase totals = $934.22       $1,031.8110   $1,031.80   $1,031.80   $1,031.90