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 $68.54   11.565%   $76.4667   $76.47   $76.45   $76.50  
  Purchase #2 $26.31   5.299%   $27.7042   $27.70   $27.70   $27.70  
  Purchase #3 $241.41   6.458%   $257.0003   $257.00   $257.00   $257.00  
  Purchase #4 $193.30   7.323%   $207.4554   $207.46   $207.45   $207.50  
  Purchase #5 $47.44   8.594%   $51.517   $51.52   $51.50   $51.50  
  Purchase #6 $181.52   13.171%   $205.428   $205.43   $205.45   $205.40  
  Purchase #7 $10.86   6.724%   $11.5902   $11.59   $11.60   $11.60  
  7 purchase totals = $769.38       $837.1618   $837.17   $837.15   $837.20