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 $154.57   6.310%   $164.3234   $164.32   $164.30   $164.30  
  Purchase #2 $248.73   6.529%   $264.9696   $264.97   $264.95   $265.00  
  Purchase #3 $33.25   8.840%   $36.1893   $36.19   $36.20   $36.20  
  Purchase #4 $153.77   4.847%   $161.2232   $161.22   $161.20   $161.20  
  Purchase #5 $239.48   12.366%   $269.0941   $269.09   $269.10   $269.10  
  Purchase #6 $104.50   10.159%   $115.1162   $115.12   $115.10   $115.10  
  Purchase #7 $148.33   6.763%   $158.3616   $158.36   $158.35   $158.40  
  7 purchase totals = $1,082.63       $1,169.2774   $1,169.27   $1,169.20   $1,169.30