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 $162.32   13.748%   $184.6358   $184.64   $184.65   $184.60  
  Purchase #2 $207.71   9.616%   $227.6834   $227.68   $227.70   $227.70  
  Purchase #3 $54.33   5.782%   $57.4714   $57.47   $57.45   $57.50  
  Purchase #4 $36.92   8.353%   $40.0039   $40.00   $40.00   $40.00  
  Purchase #5 $218.57   9.543%   $239.4281   $239.43   $239.45   $239.40  
  Purchase #6 $245.42   5.198%   $258.1769   $258.18   $258.20   $258.20  
  Purchase #7 $105.81   4.793%   $110.8815   $110.88   $110.90   $110.90  
  7 purchase totals = $1,031.08       $1,118.2810   $1,118.28   $1,118.35   $1,118.30