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 $239.34   12.627%   $269.5615   $269.56   $269.55   $269.60  
  Purchase #2 $94.49   4.195%   $98.4539   $98.45   $98.45   $98.50  
  Purchase #3 $215.65   6.679%   $230.0533   $230.05   $230.05   $230.10  
  Purchase #4 $88.80   9.587%   $97.3133   $97.31   $97.30   $97.30  
  Purchase #5 $168.85   4.567%   $176.5614   $176.56   $176.55   $176.60  
  Purchase #6 $104.80   12.472%   $117.8707   $117.87   $117.85   $117.90  
  Purchase #7 $63.25   4.811%   $66.293   $66.29   $66.30   $66.30  
  7 purchase totals = $975.18       $1,056.1071   $1,056.09   $1,056.05   $1,056.30