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 $212.33   11.315%   $236.3551   $236.36   $236.35   $236.40  
  Purchase #2 $74.56   7.211%   $79.9365   $79.94   $79.95   $79.90  
  Purchase #3 $160.99   8.727%   $175.0396   $175.04   $175.05   $175.00  
  Purchase #4 $164.42   11.458%   $183.2592   $183.26   $183.25   $183.30  
  Purchase #5 $17.61   9.483%   $19.28   $19.28   $19.30   $19.30  
  Purchase #6 $145.84   12.260%   $163.72   $163.72   $163.70   $163.70  
  Purchase #7 $196.98   4.435%   $205.7161   $205.72   $205.70   $205.70  
  7 purchase totals = $972.73       $1,063.3065   $1,063.32   $1,063.30   $1,063.30