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 $58.27   8.202%   $63.0493   $63.05   $63.05   $63.00  
  Purchase #2 $217.89   6.194%   $231.3861   $231.39   $231.40   $231.40  
  Purchase #3 $180.87   5.608%   $191.0132   $191.01   $191.00   $191.00  
  Purchase #4 $105.90   11.249%   $117.8127   $117.81   $117.80   $117.80  
  Purchase #5 $243.40   7.703%   $262.1491   $262.15   $262.15   $262.10  
  Purchase #6 $121.80   7.213%   $130.5854   $130.59   $130.60   $130.60  
  Purchase #7 $152.93   13.476%   $173.5388   $173.54   $173.55   $173.50  
  7 purchase totals = $1,081.06       $1,169.5346   $1,169.54   $1,169.55   $1,169.40