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 $175.88   12.468%   $197.8087   $197.81   $197.80   $197.80  
  Purchase #2 $159.73   11.213%   $177.6405   $177.64   $177.65   $177.60  
  Purchase #3 $37.50   9.716%   $41.1435   $41.14   $41.15   $41.10  
  Purchase #4 $226.86   4.446%   $236.9462   $236.95   $236.95   $236.90  
  Purchase #5 $169.52   4.326%   $176.8534   $176.85   $176.85   $176.90  
  Purchase #6 $240.63   13.463%   $273.026   $273.03   $273.05   $273.00  
  Purchase #7 $95.91   3.493%   $99.2601   $99.26   $99.25   $99.30  
  7 purchase totals = $1,106.03       $1,202.6784   $1,202.68   $1,202.70   $1,202.60