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 $44.68   11.183%   $49.6766   $49.68   $49.70   $49.70  
  Purchase #2 $157.74   3.353%   $163.029   $163.03   $163.05   $163.00  
  Purchase #3 $50.94   13.498%   $57.8159   $57.82   $57.80   $57.80  
  Purchase #4 $190.84   4.145%   $198.7503   $198.75   $198.75   $198.80  
  Purchase #5 $49.32   5.232%   $51.9004   $51.90   $51.90   $51.90  
  Purchase #6 $115.42   7.803%   $124.4262   $124.43   $124.45   $124.40  
  Purchase #7 $92.65   3.866%   $96.2318   $96.23   $96.25   $96.20  
  7 purchase totals = $701.59       $741.8302   $741.84   $741.90   $741.80