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 $61.57   10.294%   $67.908   $67.91   $67.90   $67.90  
  Purchase #2 $112.93   4.119%   $117.5816   $117.58   $117.60   $117.60  
  Purchase #3 $59.25   8.839%   $64.4871   $64.49   $64.50   $64.50  
  Purchase #4 $23.41   3.120%   $24.1404   $24.14   $24.15   $24.10  
  Purchase #5 $39.50   11.189%   $43.9197   $43.92   $43.90   $43.90  
  Purchase #6 $167.36   3.632%   $173.4385   $173.44   $173.45   $173.40  
  Purchase #7 $228.59   10.574%   $252.7611   $252.76   $252.75   $252.80  
  7 purchase totals = $692.61       $744.2364   $744.24   $744.25   $744.20