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 $184.44   10.177%   $203.2105   $203.21   $203.20   $203.20  
  Purchase #2 $163.38   13.758%   $185.8578   $185.86   $185.85   $185.90  
  Purchase #3 $16.52   8.783%   $17.971   $17.97   $17.95   $18.00  
  Purchase #4 $214.91   4.636%   $224.8732   $224.87   $224.85   $224.90  
  Purchase #5 $86.29   11.201%   $95.9553   $95.96   $95.95   $96.00  
  Purchase #6 $233.64   10.176%   $257.4152   $257.42   $257.40   $257.40  
  Purchase #7 $177.52   11.493%   $197.9224   $197.92   $197.90   $197.90  
  7 purchase totals = $1,076.70       $1,183.2054   $1,183.21   $1,183.10   $1,183.30