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 $203.70   3.598%   $211.0291   $211.03   $211.05   $211.00  
  Purchase #2 $148.67   12.149%   $166.7319   $166.73   $166.75   $166.70  
  Purchase #3 $218.69   8.654%   $237.6154   $237.62   $237.60   $237.60  
  Purchase #4 $170.85   8.416%   $185.2287   $185.23   $185.25   $185.20  
  Purchase #5 $73.27   10.636%   $81.063   $81.06   $81.05   $81.10  
  Purchase #6 $250.59   4.873%   $262.8013   $262.80   $262.80   $262.80  
  Purchase #7 $98.28   7.631%   $105.7797   $105.78   $105.80   $105.80  
  7 purchase totals = $1,164.05       $1,250.2491   $1,250.25   $1,250.30   $1,250.20