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 $56.76   7.824%   $61.2009   $61.20   $61.20   $61.20  
  Purchase #2 $63.36   5.443%   $66.8087   $66.81   $66.80   $66.80  
  Purchase #3 $226.34   3.406%   $234.0491   $234.05   $234.05   $234.00  
  Purchase #4 $168.80   6.867%   $180.3915   $180.39   $180.40   $180.40  
  Purchase #5 $236.81   7.685%   $255.0088   $255.01   $255.00   $255.00  
  Purchase #6 $51.46   11.148%   $57.1968   $57.20   $57.20   $57.20  
  Purchase #7 $183.79   12.295%   $206.387   $206.39   $206.40   $206.40  
  7 purchase totals = $987.32       $1,061.0428   $1,061.05   $1,061.05   $1,061.00