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 $61.68   8.188%   $66.7304   $66.73   $66.75   $66.70  
  Purchase #2 $176.31   12.432%   $198.2289   $198.23   $198.25   $198.20  
  Purchase #3 $74.57   13.406%   $84.5669   $84.57   $84.55   $84.60  
  Purchase #4 $136.41   13.781%   $155.2087   $155.21   $155.20   $155.20  
  Purchase #5 $10.61   10.556%   $11.73   $11.73   $11.75   $11.70  
  Purchase #6 $177.37   6.157%   $188.2907   $188.29   $188.30   $188.30  
  Purchase #7 $62.74   5.255%   $66.037   $66.04   $66.05   $66.00  
  7 purchase totals = $699.69       $770.7926   $770.80   $770.85   $770.70