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 $61.28   13.680%   $69.6631   $69.66   $69.65   $69.70  
  Purchase #2 $208.73   6.433%   $222.1576   $222.16   $222.15   $222.20  
  Purchase #3 $164.85   7.647%   $177.4561   $177.46   $177.45   $177.50  
  Purchase #4 $145.68   4.817%   $152.6974   $152.70   $152.70   $152.70  
  Purchase #5 $170.68   8.332%   $184.9011   $184.90   $184.90   $184.90  
  Purchase #6 $143.44   13.297%   $162.5132   $162.51   $162.50   $162.50  
  Purchase #7 $226.62   9.843%   $248.9262   $248.93   $248.95   $248.90  
  7 purchase totals = $1,121.28       $1,218.3147   $1,218.32   $1,218.30   $1,218.40