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 $104.65   10.782%   $115.9334   $115.93   $115.95   $115.90  
  Purchase #2 $141.73   11.870%   $158.5534   $158.55   $158.55   $158.60  
  Purchase #3 $218.94   4.728%   $229.2915   $229.29   $229.30   $229.30  
  Purchase #4 $23.74   10.578%   $26.2512   $26.25   $26.25   $26.30  
  Purchase #5 $230.82   7.799%   $248.8217   $248.82   $248.80   $248.80  
  Purchase #6 $50.61   12.634%   $57.0041   $57.00   $57.00   $57.00  
  Purchase #7 $217.62   6.568%   $231.9133   $231.91   $231.90   $231.90  
  7 purchase totals = $988.11       $1,067.7686   $1,067.75   $1,067.75   $1,067.80