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 $216.39   10.699%   $239.5416   $239.54   $239.55   $239.50  
  Purchase #2 $66.76   6.670%   $71.2129   $71.21   $71.20   $71.20  
  Purchase #3 $151.91   12.566%   $170.999   $171.00   $171.00   $171.00  
  Purchase #4 $219.66   10.874%   $243.5458   $243.55   $243.55   $243.50  
  Purchase #5 $40.76   6.795%   $43.5296   $43.53   $43.55   $43.50  
  Purchase #6 $59.43   10.825%   $65.8633   $65.86   $65.85   $65.90  
  Purchase #7 $181.95   6.298%   $193.4092   $193.41   $193.40   $193.40  
  7 purchase totals = $936.86       $1,028.1014   $1,028.10   $1,028.10   $1,028.00