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 $144.97   12.582%   $163.2101   $163.21   $163.20   $163.20  
  Purchase #2 $144.25   6.320%   $153.3666   $153.37   $153.35   $153.40  
  Purchase #3 $248.55   8.348%   $269.299   $269.30   $269.30   $269.30  
  Purchase #4 $237.34   13.734%   $269.9363   $269.94   $269.95   $269.90  
  Purchase #5 $161.98   6.244%   $172.094   $172.09   $172.10   $172.10  
  Purchase #6 $164.50   10.865%   $182.3729   $182.37   $182.35   $182.40  
  Purchase #7 $168.76   9.543%   $184.8648   $184.86   $184.85   $184.90  
  7 purchase totals = $1,270.35       $1,395.1437   $1,395.14   $1,395.10   $1,395.20