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 $204.29   13.685%   $232.2471   $232.25   $232.25   $232.20  
  Purchase #2 $250.54   13.622%   $284.6686   $284.67   $284.65   $284.70  
  Purchase #3 $54.64   6.715%   $58.3091   $58.31   $58.30   $58.30  
  Purchase #4 $125.41   3.133%   $129.3391   $129.34   $129.35   $129.30  
  Purchase #5 $133.93   5.620%   $141.4569   $141.46   $141.45   $141.50  
  Purchase #6 $128.90   10.611%   $142.5776   $142.58   $142.60   $142.60  
  Purchase #7 $226.75   11.435%   $252.6789   $252.68   $252.70   $252.70  
  7 purchase totals = $1,124.46       $1,241.2773   $1,241.29   $1,241.30   $1,241.30