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 $109.74   8.597%   $119.1743   $119.17   $119.15   $119.20  
  Purchase #2 $56.48   6.350%   $60.0665   $60.07   $60.05   $60.10  
  Purchase #3 $233.51   3.469%   $241.6105   $241.61   $241.60   $241.60  
  Purchase #4 $149.96   4.169%   $156.2118   $156.21   $156.20   $156.20  
  Purchase #5 $216.73   11.727%   $242.1459   $242.15   $242.15   $242.10  
  Purchase #6 $141.78   12.116%   $158.9581   $158.96   $158.95   $159.00  
  Purchase #7 $208.53   10.569%   $230.5695   $230.57   $230.55   $230.60  
  7 purchase totals = $1,116.73       $1,208.7366   $1,208.74   $1,208.65   $1,208.80