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 $205.95   11.747%   $230.1429   $230.14   $230.15   $230.10  
  Purchase #2 $167.93   3.552%   $173.8949   $173.89   $173.90   $173.90  
  Purchase #3 $105.57   8.869%   $114.933   $114.93   $114.95   $114.90  
  Purchase #4 $108.95   8.527%   $118.2402   $118.24   $118.25   $118.20  
  Purchase #5 $63.27   10.696%   $70.0374   $70.04   $70.05   $70.00  
  Purchase #6 $93.58   13.455%   $106.1712   $106.17   $106.15   $106.20  
  Purchase #7 $207.77   4.823%   $217.7907   $217.79   $217.80   $217.80  
  7 purchase totals = $953.02       $1,031.2103   $1,031.20   $1,031.25   $1,031.10