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 $67.62   8.261%   $73.2061   $73.21   $73.20   $73.20  
  Purchase #2 $227.80   10.862%   $252.5436   $252.54   $252.55   $252.50  
  Purchase #3 $169.51   5.312%   $178.5144   $178.51   $178.50   $178.50  
  Purchase #4 $27.62   7.784%   $29.7699   $29.77   $29.75   $29.80  
  Purchase #5 $246.58   6.396%   $262.3513   $262.35   $262.35   $262.40  
  Purchase #6 $114.77   13.111%   $129.8175   $129.82   $129.80   $129.80  
  Purchase #7 $243.32   13.428%   $275.993   $275.99   $276.00   $276.00  
  7 purchase totals = $1,097.22       $1,202.1958   $1,202.19   $1,202.15   $1,202.20