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 $88.65   5.864%   $93.8484   $93.85   $93.85   $93.80  
  Purchase #2 $185.58   12.388%   $208.5697   $208.57   $208.55   $208.60  
  Purchase #3 $25.44   4.593%   $26.6085   $26.61   $26.60   $26.60  
  Purchase #4 $219.68   4.440%   $229.4338   $229.43   $229.45   $229.40  
  Purchase #5 $82.40   4.223%   $85.8798   $85.88   $85.90   $85.90  
  Purchase #6 $47.67   7.293%   $51.1466   $51.15   $51.15   $51.10  
  Purchase #7 $129.54   5.687%   $136.9069   $136.91   $136.90   $136.90  
  7 purchase totals = $778.96       $832.3937   $832.40   $832.40   $832.30