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 $46.60   13.564%   $52.9208   $52.92   $52.90   $52.90  
  Purchase #2 $228.87   3.546%   $236.9857   $236.99   $237.00   $237.00  
  Purchase #3 $238.43   4.703%   $249.6434   $249.64   $249.65   $249.60  
  Purchase #4 $13.41   10.244%   $14.7837   $14.78   $14.80   $14.80  
  Purchase #5 $123.55   8.561%   $134.1271   $134.13   $134.15   $134.10  
  Purchase #6 $71.40   7.493%   $76.75   $76.75   $76.75   $76.80  
  Purchase #7 $169.25   10.500%   $187.0213   $187.02   $187.00   $187.00  
  7 purchase totals = $891.51       $952.2320   $952.23   $952.25   $952.20