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 $190.63   6.757%   $203.5109   $203.51   $203.50   $203.50  
  Purchase #2 $242.38   3.138%   $249.9859   $249.99   $250.00   $250.00  
  Purchase #3 $60.30   5.120%   $63.3874   $63.39   $63.40   $63.40  
  Purchase #4 $67.50   6.254%   $71.7215   $71.72   $71.70   $71.70  
  Purchase #5 $134.63   13.748%   $153.1389   $153.14   $153.15   $153.10  
  Purchase #6 $12.93   13.407%   $14.6635   $14.66   $14.65   $14.70  
  Purchase #7 $226.49   11.408%   $252.328   $252.33   $252.35   $252.30  
  7 purchase totals = $934.86       $1,008.7361   $1,008.74   $1,008.75   $1,008.70