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 $243.83   10.451%   $269.3127   $269.31   $269.30   $269.30  
  Purchase #2 $220.95   13.118%   $249.9342   $249.93   $249.95   $249.90  
  Purchase #3 $116.83   6.202%   $124.0758   $124.08   $124.10   $124.10  
  Purchase #4 $169.48   13.737%   $192.7615   $192.76   $192.75   $192.80  
  Purchase #5 $87.51   12.478%   $98.4295   $98.43   $98.45   $98.40  
  Purchase #6 $6.87   6.372%   $7.3078   $7.31   $7.30   $7.30  
  Purchase #7 $37.36   10.872%   $41.4218   $41.42   $41.40   $41.40  
  7 purchase totals = $882.83       $983.2433   $983.24   $983.25   $983.20