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 $54.70   4.215%   $57.0056   $57.01   $57.00   $57.00  
  Purchase #2 $241.72   9.309%   $264.2217   $264.22   $264.20   $264.20  
  Purchase #3 $126.25   13.253%   $142.9819   $142.98   $143.00   $143.00  
  Purchase #4 $188.28   3.307%   $194.5064   $194.51   $194.50   $194.50  
  Purchase #5 $157.58   11.292%   $175.3739   $175.37   $175.35   $175.40  
  Purchase #6 $143.47   5.781%   $151.764   $151.76   $151.75   $151.80  
  Purchase #7 $71.77   13.159%   $81.2142   $81.21   $81.20   $81.20  
  7 purchase totals = $983.77       $1,067.0677   $1,067.06   $1,067.00   $1,067.10