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 $240.87   11.640%   $268.9073   $268.91   $268.90   $268.90  
  Purchase #2 $116.32   6.672%   $124.0809   $124.08   $124.10   $124.10  
  Purchase #3 $176.77   3.521%   $182.9941   $182.99   $183.00   $183.00  
  Purchase #4 $64.55   8.252%   $69.8767   $69.88   $69.90   $69.90  
  Purchase #5 $112.25   9.658%   $123.0911   $123.09   $123.10   $123.10  
  Purchase #6 $179.41   4.714%   $187.8674   $187.87   $187.85   $187.90  
  Purchase #7 $131.67   6.859%   $140.7012   $140.70   $140.70   $140.70  
  7 purchase totals = $1,021.84       $1,097.5187   $1,097.52   $1,097.55   $1,097.60