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 $50.60   11.162%   $56.248   $56.25   $56.25   $56.20  
  Purchase #2 $163.94   4.314%   $171.0124   $171.01   $171.00   $171.00  
  Purchase #3 $48.64   11.712%   $54.3367   $54.34   $54.35   $54.30  
  Purchase #4 $61.28   6.704%   $65.3882   $65.39   $65.40   $65.40  
  Purchase #5 $86.96   11.865%   $97.2778   $97.28   $97.30   $97.30  
  Purchase #6 $239.33   3.730%   $248.257   $248.26   $248.25   $248.30  
  Purchase #7 $62.37   4.405%   $65.1174   $65.12   $65.10   $65.10  
  7 purchase totals = $713.12       $757.6375   $757.65   $757.65   $757.60