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 $224.59   10.836%   $248.9266   $248.93   $248.95   $248.90  
  Purchase #2 $116.30   10.661%   $128.6987   $128.70   $128.70   $128.70  
  Purchase #3 $134.96   12.563%   $151.915   $151.92   $151.90   $151.90  
  Purchase #4 $127.39   5.206%   $134.0219   $134.02   $134.00   $134.00  
  Purchase #5 $183.49   9.695%   $201.2794   $201.28   $201.30   $201.30  
  Purchase #6 $94.25   7.862%   $101.6599   $101.66   $101.65   $101.70  
  Purchase #7 $93.51   4.540%   $97.7554   $97.76   $97.75   $97.80  
  7 purchase totals = $974.49       $1,064.2569   $1,064.27   $1,064.25   $1,064.30