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 $156.62   10.608%   $173.2342   $173.23   $173.25   $173.20  
  Purchase #2 $146.81   5.756%   $155.2604   $155.26   $155.25   $155.30  
  Purchase #3 $154.75   9.211%   $169.004   $169.00   $169.00   $169.00  
  Purchase #4 $104.82   9.482%   $114.759   $114.76   $114.75   $114.80  
  Purchase #5 $226.26   3.851%   $234.9733   $234.97   $234.95   $235.00  
  Purchase #6 $163.59   5.663%   $172.8541   $172.85   $172.85   $172.90  
  Purchase #7 $142.95   10.118%   $157.4137   $157.41   $157.40   $157.40  
  7 purchase totals = $1,095.80       $1,177.4987   $1,177.48   $1,177.45   $1,177.60