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 $24.85   5.682%   $26.262   $26.26   $26.25   $26.30  
  Purchase #2 $19.65   7.483%   $21.1204   $21.12   $21.10   $21.10  
  Purchase #3 $106.77   8.867%   $116.2373   $116.24   $116.25   $116.20  
  Purchase #4 $142.96   9.194%   $156.1037   $156.10   $156.10   $156.10  
  Purchase #5 $242.56   10.441%   $267.8857   $267.89   $267.90   $267.90  
  Purchase #6 $189.42   10.246%   $208.828   $208.83   $208.85   $208.80  
  Purchase #7 $148.71   11.591%   $165.947   $165.95   $165.95   $165.90  
  7 purchase totals = $874.92       $962.3841   $962.39   $962.40   $962.30