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 $97.30   10.479%   $107.4961   $107.50   $107.50   $107.50  
  Purchase #2 $45.36   5.788%   $47.9854   $47.99   $48.00   $48.00  
  Purchase #3 $183.79   11.850%   $205.5691   $205.57   $205.55   $205.60  
  Purchase #4 $219.39   8.334%   $237.674   $237.67   $237.65   $237.70  
  Purchase #5 $134.57   7.871%   $145.162   $145.16   $145.15   $145.20  
  Purchase #6 $114.37   13.413%   $129.7104   $129.71   $129.70   $129.70  
  Purchase #7 $196.83   8.512%   $213.5842   $213.58   $213.60   $213.60  
  7 purchase totals = $991.61       $1,087.1812   $1,087.18   $1,087.15   $1,087.30