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 $60.32   4.724%   $63.1695   $63.17   $63.15   $63.20  
  Purchase #2 $219.94   6.149%   $233.4641   $233.46   $233.45   $233.50  
  Purchase #3 $163.47   8.709%   $177.7066   $177.71   $177.70   $177.70  
  Purchase #4 $181.53   6.762%   $193.8051   $193.81   $193.80   $193.80  
  Purchase #5 $234.66   13.201%   $265.6375   $265.64   $265.65   $265.60  
  Purchase #6 $234.68   4.388%   $244.9778   $244.98   $245.00   $245.00  
  Purchase #7 $155.54   12.819%   $175.4787   $175.48   $175.50   $175.50  
  7 purchase totals = $1,250.14       $1,354.2393   $1,354.25   $1,354.25   $1,354.30