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 $247.44   6.162%   $262.6873   $262.69   $262.70   $262.70  
  Purchase #2 $236.42   6.135%   $250.9244   $250.92   $250.90   $250.90  
  Purchase #3 $51.93   5.558%   $54.8163   $54.82   $54.80   $54.80  
  Purchase #4 $99.39   11.592%   $110.9113   $110.91   $110.90   $110.90  
  Purchase #5 $139.45   8.361%   $151.1094   $151.11   $151.10   $151.10  
  Purchase #6 $221.79   4.718%   $232.2541   $232.25   $232.25   $232.30  
  Purchase #7 $184.58   6.719%   $196.9819   $196.98   $197.00   $197.00  
  7 purchase totals = $1,181.00       $1,259.6847   $1,259.68   $1,259.65   $1,259.70