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 $20.63   7.340%   $22.1442   $22.14   $22.15   $22.10  
  Purchase #2 $115.80   4.460%   $120.9647   $120.96   $120.95   $121.00  
  Purchase #3 $70.96   12.308%   $79.6938   $79.69   $79.70   $79.70  
  Purchase #4 $176.43   3.648%   $182.8662   $182.87   $182.85   $182.90  
  Purchase #5 $186.50   12.641%   $210.0755   $210.08   $210.10   $210.10  
  Purchase #6 $108.47   5.366%   $114.2905   $114.29   $114.30   $114.30  
  Purchase #7 $158.26   13.340%   $179.3719   $179.37   $179.35   $179.40  
  7 purchase totals = $837.05       $909.4068   $909.40   $909.40   $909.50