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 $24.66   6.771%   $26.3297   $26.33   $26.35   $26.30  
  Purchase #2 $206.31   4.608%   $215.8168   $215.82   $215.80   $215.80  
  Purchase #3 $8.76   3.343%   $9.0528   $9.05   $9.05   $9.10  
  Purchase #4 $60.96   3.389%   $63.0259   $63.03   $63.05   $63.00  
  Purchase #5 $182.76   13.515%   $207.46   $207.46   $207.45   $207.50  
  Purchase #6 $71.78   12.274%   $80.5903   $80.59   $80.60   $80.60  
  Purchase #7 $112.40   8.390%   $121.8304   $121.83   $121.85   $121.80  
  7 purchase totals = $667.63       $724.1059   $724.11   $724.15   $724.10