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 $28.79   4.712%   $30.1466   $30.15   $30.15   $30.10  
  Purchase #2 $123.63   4.721%   $129.4666   $129.47   $129.45   $129.50  
  Purchase #3 $6.33   10.349%   $6.9851   $6.99   $7.00   $7.00  
  Purchase #4 $140.44   8.244%   $152.0179   $152.02   $152.00   $152.00  
  Purchase #5 $223.82   4.414%   $233.6994   $233.70   $233.70   $233.70  
  Purchase #6 $200.53   11.478%   $223.5468   $223.55   $223.55   $223.50  
  Purchase #7 $102.82   3.619%   $106.5411   $106.54   $106.55   $106.50  
  7 purchase totals = $826.36       $882.4035   $882.42   $882.40   $882.30