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 $82.31   13.509%   $93.4293   $93.43   $93.45   $93.40  
  Purchase #2 $33.50   4.730%   $35.0846   $35.08   $35.10   $35.10  
  Purchase #3 $170.76   13.147%   $193.2098   $193.21   $193.20   $193.20  
  Purchase #4 $85.51   8.804%   $93.0383   $93.04   $93.05   $93.00  
  Purchase #5 $178.66   9.822%   $196.208   $196.21   $196.20   $196.20  
  Purchase #6 $92.29   3.836%   $95.8302   $95.83   $95.85   $95.80  
  Purchase #7 $46.90   8.163%   $50.7284   $50.73   $50.75   $50.70  
  7 purchase totals = $689.93       $757.5286   $757.53   $757.60   $757.40