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 $243.98   10.468%   $269.5198   $269.52   $269.50   $269.50  
  Purchase #2 $81.27   6.266%   $86.3624   $86.36   $86.35   $86.40  
  Purchase #3 $226.49   5.141%   $238.1339   $238.13   $238.15   $238.10  
  Purchase #4 $212.77   12.401%   $239.1556   $239.16   $239.15   $239.20  
  Purchase #5 $55.76   13.775%   $63.4409   $63.44   $63.45   $63.40  
  Purchase #6 $190.84   7.216%   $204.611   $204.61   $204.60   $204.60  
  Purchase #7 $138.58   10.794%   $153.5383   $153.54   $153.55   $153.50  
  7 purchase totals = $1,149.69       $1,254.7619   $1,254.76   $1,254.75   $1,254.70