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 $208.25   11.546%   $232.2945   $232.29   $232.30   $232.30  
  Purchase #2 $64.59   13.703%   $73.4408   $73.44   $73.45   $73.40  
  Purchase #3 $140.45   9.130%   $153.2731   $153.27   $153.25   $153.30  
  Purchase #4 $46.93   6.454%   $49.9589   $49.96   $49.95   $50.00  
  Purchase #5 $224.51   10.443%   $247.9556   $247.96   $247.95   $248.00  
  Purchase #6 $226.89   10.852%   $251.5121   $251.51   $251.50   $251.50  
  Purchase #7 $163.83   8.861%   $178.347   $178.35   $178.35   $178.30  
  7 purchase totals = $1,075.45       $1,186.7820   $1,186.78   $1,186.75   $1,186.80