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 $196.50   4.827%   $205.9851   $205.99   $206.00   $206.00  
  Purchase #2 $33.60   3.273%   $34.6997   $34.70   $34.70   $34.70  
  Purchase #3 $218.58   8.195%   $236.4926   $236.49   $236.50   $236.50  
  Purchase #4 $59.51   4.385%   $62.1195   $62.12   $62.10   $62.10  
  Purchase #5 $167.66   5.806%   $177.3943   $177.39   $177.40   $177.40  
  Purchase #6 $111.62   12.307%   $125.3571   $125.36   $125.35   $125.40  
  Purchase #7 $194.96   3.239%   $201.2748   $201.27   $201.25   $201.30  
  7 purchase totals = $982.43       $1,043.3231   $1,043.32   $1,043.30   $1,043.40