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 $226.46   10.470%   $250.1704   $250.17   $250.15   $250.20  
  Purchase #2 $178.84   3.438%   $184.9885   $184.99   $185.00   $185.00  
  Purchase #3 $36.86   10.572%   $40.7568   $40.76   $40.75   $40.80  
  Purchase #4 $208.74   5.773%   $220.7906   $220.79   $220.80   $220.80  
  Purchase #5 $219.91   6.253%   $233.661   $233.66   $233.65   $233.70  
  Purchase #6 $41.64   9.140%   $45.4459   $45.45   $45.45   $45.40  
  Purchase #7 $232.41   3.676%   $240.9534   $240.95   $240.95   $241.00  
  7 purchase totals = $1,144.86       $1,216.7666   $1,216.77   $1,216.75   $1,216.90