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 $186.72   8.174%   $201.9825   $201.98   $202.00   $202.00  
  Purchase #2 $180.59   3.521%   $186.9486   $186.95   $186.95   $186.90  
  Purchase #3 $82.31   7.662%   $88.6166   $88.62   $88.60   $88.60  
  Purchase #4 $175.64   4.588%   $183.6984   $183.70   $183.70   $183.70  
  Purchase #5 $180.54   7.857%   $194.725   $194.73   $194.75   $194.70  
  Purchase #6 $72.26   9.863%   $79.387   $79.39   $79.40   $79.40  
  Purchase #7 $106.47   7.449%   $114.401   $114.40   $114.40   $114.40  
  7 purchase totals = $984.53       $1,049.7591   $1,049.77   $1,049.80   $1,049.70