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 $27.81   6.361%   $29.579   $29.58   $29.60   $29.60  
  Purchase #2 $178.92   6.753%   $191.0025   $191.00   $191.00   $191.00  
  Purchase #3 $118.47   9.639%   $129.8893   $129.89   $129.90   $129.90  
  Purchase #4 $148.64   3.764%   $154.2348   $154.23   $154.25   $154.20  
  Purchase #5 $212.36   6.712%   $226.6136   $226.61   $226.60   $226.60  
  Purchase #6 $152.30   4.330%   $158.8946   $158.89   $158.90   $158.90  
  Purchase #7 $164.64   5.565%   $173.8022   $173.80   $173.80   $173.80  
  7 purchase totals = $1,003.14       $1,064.0160   $1,064.00   $1,064.05   $1,064.00