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 $236.25   11.250%   $262.8281   $262.83   $262.85   $262.80  
  Purchase #2 $178.25   9.559%   $195.2889   $195.29   $195.30   $195.30  
  Purchase #3 $168.93   6.225%   $179.4459   $179.45   $179.45   $179.40  
  Purchase #4 $161.67   10.564%   $178.7488   $178.75   $178.75   $178.70  
  Purchase #5 $53.58   6.214%   $56.9095   $56.91   $56.90   $56.90  
  Purchase #6 $26.39   11.602%   $29.4518   $29.45   $29.45   $29.50  
  Purchase #7 $146.28   10.575%   $161.7491   $161.75   $161.75   $161.70  
  7 purchase totals = $971.35       $1,064.4221   $1,064.43   $1,064.45   $1,064.30