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 $24.32   10.597%   $26.8972   $26.90   $26.90   $26.90  
  Purchase #2 $248.87   9.457%   $272.4056   $272.41   $272.40   $272.40  
  Purchase #3 $70.54   4.574%   $73.7665   $73.77   $73.75   $73.80  
  Purchase #4 $162.42   6.678%   $173.2664   $173.27   $173.25   $173.30  
  Purchase #5 $120.71   11.127%   $134.1414   $134.14   $134.15   $134.10  
  Purchase #6 $91.62   8.866%   $99.743   $99.74   $99.75   $99.70  
  Purchase #7 $240.61   12.128%   $269.7912   $269.79   $269.80   $269.80  
  7 purchase totals = $959.09       $1,050.0113   $1,050.02   $1,050.00   $1,050.00