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 $30.26   7.645%   $32.5734   $32.57   $32.55   $32.60  
  Purchase #2 $165.62   11.694%   $184.9876   $184.99   $185.00   $185.00  
  Purchase #3 $165.28   6.592%   $176.1753   $176.18   $176.20   $176.20  
  Purchase #4 $219.57   3.768%   $227.8434   $227.84   $227.85   $227.80  
  Purchase #5 $35.51   4.594%   $37.1413   $37.14   $37.15   $37.10  
  Purchase #6 $241.55   9.717%   $265.0214   $265.02   $265.00   $265.00  
  Purchase #7 $106.28   7.311%   $114.0501   $114.05   $114.05   $114.10  
  7 purchase totals = $964.07       $1,037.7925   $1,037.79   $1,037.80   $1,037.80