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 $141.97   11.120%   $157.7571   $157.76   $157.75   $157.80  
  Purchase #2 $179.75   12.765%   $202.6951   $202.70   $202.70   $202.70  
  Purchase #3 $249.47   4.114%   $259.7332   $259.73   $259.75   $259.70  
  Purchase #4 $131.79   5.662%   $139.2519   $139.25   $139.25   $139.30  
  Purchase #5 $160.84   9.512%   $176.1391   $176.14   $176.15   $176.10  
  Purchase #6 $164.41   11.346%   $183.064   $183.06   $183.05   $183.10  
  Purchase #7 $107.54   5.568%   $113.5278   $113.53   $113.55   $113.50  
  7 purchase totals = $1,135.77       $1,232.1682   $1,232.17   $1,232.20   $1,232.20