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 $92.87   7.542%   $99.8743   $99.87   $99.85   $99.90  
  Purchase #2 $181.66   11.611%   $202.7525   $202.75   $202.75   $202.80  
  Purchase #3 $237.83   7.834%   $256.4616   $256.46   $256.45   $256.50  
  Purchase #4 $69.49   8.493%   $75.3918   $75.39   $75.40   $75.40  
  Purchase #5 $97.55   6.104%   $103.5045   $103.50   $103.50   $103.50  
  Purchase #6 $178.38   8.588%   $193.6993   $193.70   $193.70   $193.70  
  Purchase #7 $66.92   10.166%   $73.7231   $73.72   $73.70   $73.70  
  7 purchase totals = $924.70       $1,005.4071   $1,005.39   $1,005.35   $1,005.50