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 $192.27   4.866%   $201.6259   $201.63   $201.65   $201.60  
  Purchase #2 $145.59   8.179%   $157.4978   $157.50   $157.50   $157.50  
  Purchase #3 $33.32   11.624%   $37.1931   $37.19   $37.20   $37.20  
  Purchase #4 $14.53   10.617%   $16.0727   $16.07   $16.05   $16.10  
  Purchase #5 $11.54   7.724%   $12.4313   $12.43   $12.45   $12.40  
  Purchase #6 $236.52   4.854%   $248.0007   $248.00   $248.00   $248.00  
  Purchase #7 $230.33   10.563%   $254.6598   $254.66   $254.65   $254.70  
  7 purchase totals = $864.10       $927.4813   $927.48   $927.50   $927.50