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 $87.43   10.296%   $96.4318   $96.43   $96.45   $96.40  
  Purchase #2 $203.68   9.147%   $222.3106   $222.31   $222.30   $222.30  
  Purchase #3 $114.87   4.303%   $119.8129   $119.81   $119.80   $119.80  
  Purchase #4 $234.70   7.730%   $252.8423   $252.84   $252.85   $252.80  
  Purchase #5 $202.58   11.213%   $225.2953   $225.30   $225.30   $225.30  
  Purchase #6 $226.82   10.644%   $250.9627   $250.96   $250.95   $251.00  
  Purchase #7 $66.63   13.616%   $75.7023   $75.70   $75.70   $75.70  
  7 purchase totals = $1,136.71       $1,243.3579   $1,243.35   $1,243.35   $1,243.30