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 $60.53   13.202%   $68.5212   $68.52   $68.50   $68.50  
  Purchase #2 $174.75   7.131%   $187.2114   $187.21   $187.20   $187.20  
  Purchase #3 $176.52   11.183%   $196.2602   $196.26   $196.25   $196.30  
  Purchase #4 $236.66   10.722%   $262.0347   $262.03   $262.05   $262.00  
  Purchase #5 $227.74   5.283%   $239.7715   $239.77   $239.75   $239.80  
  Purchase #6 $206.41   11.186%   $229.499   $229.50   $229.50   $229.50  
  Purchase #7 $104.82   8.444%   $113.671   $113.67   $113.65   $113.70  
  7 purchase totals = $1,187.43       $1,296.9690   $1,296.96   $1,296.90   $1,297.00