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 $238.61   11.704%   $266.5369   $266.54   $266.55   $266.50  
  Purchase #2 $17.42   3.809%   $18.0835   $18.08   $18.10   $18.10  
  Purchase #3 $33.87   10.830%   $37.5381   $37.54   $37.55   $37.50  
  Purchase #4 $162.86   8.488%   $176.6836   $176.68   $176.70   $176.70  
  Purchase #5 $211.36   6.460%   $225.0139   $225.01   $225.00   $225.00  
  Purchase #6 $158.33   10.464%   $174.8977   $174.90   $174.90   $174.90  
  Purchase #7 $142.98   9.592%   $156.6946   $156.69   $156.70   $156.70  
  7 purchase totals = $965.43       $1,055.4483   $1,055.44   $1,055.50   $1,055.40