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 $49.46   13.860%   $56.3152   $56.32   $56.30   $56.30  
  Purchase #2 $77.63   10.766%   $85.9876   $85.99   $86.00   $86.00  
  Purchase #3 $44.57   13.783%   $50.7131   $50.71   $50.70   $50.70  
  Purchase #4 $118.44   5.430%   $124.8713   $124.87   $124.85   $124.90  
  Purchase #5 $163.97   7.392%   $176.0907   $176.09   $176.10   $176.10  
  Purchase #6 $199.37   6.330%   $211.9901   $211.99   $212.00   $212.00  
  Purchase #7 $27.69   5.559%   $29.2293   $29.23   $29.25   $29.20  
  7 purchase totals = $681.13       $735.1973   $735.20   $735.20   $735.20