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 $223.77   11.120%   $248.6532   $248.65   $248.65   $248.70  
  Purchase #2 $223.71   10.822%   $247.9199   $247.92   $247.90   $247.90  
  Purchase #3 $205.71   8.441%   $223.074   $223.07   $223.05   $223.10  
  Purchase #4 $61.59   10.731%   $68.1992   $68.20   $68.20   $68.20  
  Purchase #5 $205.93   10.733%   $228.0325   $228.03   $228.05   $228.00  
  Purchase #6 $164.72   6.338%   $175.16   $175.16   $175.15   $175.20  
  Purchase #7 $137.79   13.367%   $156.2084   $156.21   $156.20   $156.20  
  7 purchase totals = $1,223.22       $1,347.2472   $1,347.24   $1,347.20   $1,347.30