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 $86.76   13.585%   $98.5463   $98.55   $98.55   $98.50  
  Purchase #2 $182.59   10.591%   $201.9281   $201.93   $201.95   $201.90  
  Purchase #3 $103.45   13.523%   $117.4395   $117.44   $117.45   $117.40  
  Purchase #4 $129.40   8.803%   $140.7911   $140.79   $140.80   $140.80  
  Purchase #5 $162.76   11.436%   $181.3732   $181.37   $181.35   $181.40  
  Purchase #6 $68.78   4.250%   $71.7032   $71.70   $71.70   $71.70  
  Purchase #7 $183.32   10.628%   $202.8032   $202.80   $202.80   $202.80  
  7 purchase totals = $917.06       $1,014.5846   $1,014.58   $1,014.60   $1,014.50