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 $107.83   11.791%   $120.5442   $120.54   $120.55   $120.50  
  Purchase #2 $176.64   4.492%   $184.5747   $184.57   $184.55   $184.60  
  Purchase #3 $178.62   13.593%   $202.8998   $202.90   $202.90   $202.90  
  Purchase #4 $220.40   9.563%   $241.4769   $241.48   $241.50   $241.50  
  Purchase #5 $103.53   8.646%   $112.4812   $112.48   $112.50   $112.50  
  Purchase #6 $114.55   8.458%   $124.2386   $124.24   $124.25   $124.20  
  Purchase #7 $31.54   5.241%   $33.193   $33.19   $33.20   $33.20  
  7 purchase totals = $933.11       $1,019.4084   $1,019.40   $1,019.45   $1,019.40