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 $56.82   7.446%   $61.0508   $61.05   $61.05   $61.10  
  Purchase #2 $88.68   9.368%   $96.9875   $96.99   $97.00   $97.00  
  Purchase #3 $76.33   8.261%   $82.6356   $82.64   $82.65   $82.60  
  Purchase #4 $186.32   9.688%   $204.3707   $204.37   $204.35   $204.40  
  Purchase #5 $155.88   5.664%   $164.709   $164.71   $164.70   $164.70  
  Purchase #6 $120.54   4.741%   $126.2548   $126.25   $126.25   $126.30  
  Purchase #7 $204.39   9.176%   $223.1448   $223.14   $223.15   $223.10  
  7 purchase totals = $888.96       $959.1532   $959.15   $959.15   $959.20