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 $128.44   10.473%   $141.8915   $141.89   $141.90   $141.90  
  Purchase #2 $248.69   8.444%   $269.6894   $269.69   $269.70   $269.70  
  Purchase #3 $232.46   5.495%   $245.2337   $245.23   $245.25   $245.20  
  Purchase #4 $214.61   9.679%   $235.3821   $235.38   $235.40   $235.40  
  Purchase #5 $136.98   6.448%   $145.8125   $145.81   $145.80   $145.80  
  Purchase #6 $23.76   11.638%   $26.5252   $26.53   $26.55   $26.50  
  Purchase #7 $91.85   10.691%   $101.6697   $101.67   $101.65   $101.70  
  7 purchase totals = $1,076.79       $1,166.2041   $1,166.20   $1,166.25   $1,166.20