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 $43.39   13.529%   $49.2602   $49.26   $49.25   $49.30  
  Purchase #2 $60.35   12.781%   $68.0633   $68.06   $68.05   $68.10  
  Purchase #3 $101.88   13.741%   $115.8793   $115.88   $115.90   $115.90  
  Purchase #4 $213.85   6.452%   $227.6476   $227.65   $227.65   $227.60  
  Purchase #5 $128.54   3.866%   $133.5094   $133.51   $133.50   $133.50  
  Purchase #6 $109.61   12.581%   $123.4   $123.40   $123.40   $123.40  
  Purchase #7 $54.75   7.596%   $58.9088   $58.91   $58.90   $58.90  
  7 purchase totals = $712.37       $776.6686   $776.67   $776.65   $776.70