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 $182.74   13.693%   $207.7626   $207.76   $207.75   $207.80  
  Purchase #2 $229.34   5.147%   $241.1441   $241.14   $241.15   $241.10  
  Purchase #3 $14.26   9.337%   $15.5915   $15.59   $15.60   $15.60  
  Purchase #4 $10.83   10.417%   $11.9582   $11.96   $11.95   $12.00  
  Purchase #5 $184.95   11.656%   $206.5078   $206.51   $206.50   $206.50  
  Purchase #6 $55.80   12.120%   $62.563   $62.56   $62.55   $62.60  
  Purchase #7 $42.78   8.687%   $46.4963   $46.50   $46.50   $46.50  
  7 purchase totals = $720.70       $792.0235   $792.02   $792.00   $792.10