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 $86.97   12.226%   $97.603   $97.60   $97.60   $97.60  
  Purchase #2 $117.66   6.116%   $124.8561   $124.86   $124.85   $124.90  
  Purchase #3 $73.68   4.642%   $77.1002   $77.10   $77.10   $77.10  
  Purchase #4 $142.75   13.518%   $162.0469   $162.05   $162.05   $162.00  
  Purchase #5 $100.75   7.349%   $108.1541   $108.15   $108.15   $108.20  
  Purchase #6 $62.84   5.795%   $66.4816   $66.48   $66.50   $66.50  
  Purchase #7 $233.59   10.223%   $257.4699   $257.47   $257.45   $257.50  
  7 purchase totals = $818.24       $893.7118   $893.71   $893.70   $893.80