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 $207.45   9.231%   $226.5997   $226.60   $226.60   $226.60  
  Purchase #2 $57.88   12.714%   $65.2389   $65.24   $65.25   $65.20  
  Purchase #3 $33.93   4.825%   $35.5671   $35.57   $35.55   $35.60  
  Purchase #4 $89.33   9.232%   $97.5769   $97.58   $97.60   $97.60  
  Purchase #5 $9.42   10.505%   $10.4096   $10.41   $10.40   $10.40  
  Purchase #6 $210.54   6.820%   $224.8988   $224.90   $224.90   $224.90  
  Purchase #7 $55.54   9.297%   $60.7036   $60.70   $60.70   $60.70  
  7 purchase totals = $664.09       $720.9946   $721.00   $721.00   $721.00