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 $57.68   4.850%   $60.4775   $60.48   $60.50   $60.50  
  Purchase #2 $208.43   12.556%   $234.6005   $234.60   $234.60   $234.60  
  Purchase #3 $212.81   4.669%   $222.7461   $222.75   $222.75   $222.70  
  Purchase #4 $130.83   10.240%   $144.227   $144.23   $144.25   $144.20  
  Purchase #5 $67.39   6.637%   $71.8627   $71.86   $71.85   $71.90  
  Purchase #6 $138.60   7.557%   $149.074   $149.07   $149.05   $149.10  
  Purchase #7 $168.44   5.573%   $177.8272   $177.83   $177.85   $177.80  
  7 purchase totals = $984.18       $1,060.8150   $1,060.82   $1,060.85   $1,060.80