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 $8.74   3.250%   $9.0241   $9.02   $9.00   $9.00  
  Purchase #2 $16.38   13.724%   $18.628   $18.63   $18.65   $18.60  
  Purchase #3 $148.65   10.768%   $164.6566   $164.66   $164.65   $164.70  
  Purchase #4 $191.45   10.583%   $211.7112   $211.71   $211.70   $211.70  
  Purchase #5 $173.58   9.842%   $190.6637   $190.66   $190.65   $190.70  
  Purchase #6 $148.54   11.482%   $165.5954   $165.60   $165.60   $165.60  
  Purchase #7 $47.95   6.736%   $51.1799   $51.18   $51.20   $51.20  
  7 purchase totals = $735.29       $811.4589   $811.46   $811.45   $811.50