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 $62.66   8.855%   $68.2085   $68.21   $68.20   $68.20  
  Purchase #2 $59.87   7.486%   $64.3519   $64.35   $64.35   $64.40  
  Purchase #3 $234.96   11.258%   $261.4118   $261.41   $261.40   $261.40  
  Purchase #4 $216.91   10.223%   $239.0847   $239.08   $239.10   $239.10  
  Purchase #5 $81.75   9.566%   $89.5702   $89.57   $89.55   $89.60  
  Purchase #6 $58.81   8.862%   $64.0217   $64.02   $64.00   $64.00  
  Purchase #7 $130.34   7.559%   $140.1924   $140.19   $140.20   $140.20  
  7 purchase totals = $845.30       $926.8412   $926.83   $926.80   $926.90