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 $239.35   9.553%   $262.2151   $262.22   $262.20   $262.20  
  Purchase #2 $174.47   10.753%   $193.2308   $193.23   $193.25   $193.20  
  Purchase #3 $70.45   4.637%   $73.7168   $73.72   $73.70   $73.70  
  Purchase #4 $24.90   9.857%   $27.3544   $27.35   $27.35   $27.40  
  Purchase #5 $85.46   10.611%   $94.5282   $94.53   $94.55   $94.50  
  Purchase #6 $100.41   12.547%   $113.0084   $113.01   $113.00   $113.00  
  Purchase #7 $83.92   8.852%   $91.3486   $91.35   $91.35   $91.30  
  7 purchase totals = $778.96       $855.4023   $855.41   $855.40   $855.30