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 $23.97   8.526%   $26.0137   $26.01   $26.00   $26.00  
  Purchase #2 $92.44   4.396%   $96.5037   $96.50   $96.50   $96.50  
  Purchase #3 $108.88   4.221%   $113.4758   $113.48   $113.50   $113.50  
  Purchase #4 $240.33   3.219%   $248.0662   $248.07   $248.05   $248.10  
  Purchase #5 $127.97   11.512%   $142.7019   $142.70   $142.70   $142.70  
  Purchase #6 $120.50   11.302%   $134.1189   $134.12   $134.10   $134.10  
  Purchase #7 $46.40   7.295%   $49.7849   $49.78   $49.80   $49.80  
  7 purchase totals = $760.49       $810.6651   $810.66   $810.65   $810.70