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 $38.95   12.634%   $43.8709   $43.87   $43.85   $43.90  
  Purchase #2 $222.84   11.653%   $248.8075   $248.81   $248.80   $248.80  
  Purchase #3 $164.79   6.503%   $175.5063   $175.51   $175.50   $175.50  
  Purchase #4 $155.25   5.224%   $163.3603   $163.36   $163.35   $163.40  
  Purchase #5 $61.57   5.417%   $64.9052   $64.91   $64.90   $64.90  
  Purchase #6 $227.33   12.624%   $256.0281   $256.03   $256.05   $256.00  
  Purchase #7 $69.35   8.223%   $75.0527   $75.05   $75.05   $75.10  
  7 purchase totals = $940.08       $1,027.5310   $1,027.54   $1,027.50   $1,027.60