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 $61.53   9.334%   $67.2732   $67.27   $67.25   $67.30  
  Purchase #2 $226.25   7.724%   $243.7256   $243.73   $243.75   $243.70  
  Purchase #3 $225.69   12.616%   $254.1631   $254.16   $254.15   $254.20  
  Purchase #4 $203.82   12.536%   $229.3709   $229.37   $229.35   $229.40  
  Purchase #5 $181.58   13.594%   $206.264   $206.26   $206.25   $206.30  
  Purchase #6 $53.50   8.720%   $58.1652   $58.17   $58.15   $58.20  
  Purchase #7 $60.82   4.325%   $63.4505   $63.45   $63.45   $63.50  
  7 purchase totals = $1,013.19       $1,122.4125   $1,122.41   $1,122.35   $1,122.60